Abstract
Background
Pigs are widely used as large animal models in cardiovascular research. Establishing breed-specific physiological reference values is essential for experimental design and data interpretation.
Method
Cardiac chamber dimensions, great vessel diameters, and hemodynamic parameters were systematically evaluated by transthoracic echocardiography (TTE) in 31 healthy Diannan small-ear pigs (mean weight: 47.2 ± 17.2 kg; 15 males, 16 females). Key structural indices were compared with human reference values. Animals were divided into three weight groups: 20–39 kg, 40–59 kg, and 60–80 kg.
Results
Left and right atrial and ventricular diameters and volumes, as well as aortic and pulmonary artery diameters, increased significantly with body weight (P < 0.05) but remained smaller than human reference ranges (P < 0.05). Left ventricular wall thickness exceeded human values (P < 0.05), indicating a “small-cavity, thick-wall” structural phenotype. Left ventricular ejection fraction (LVEF) did not differ significantly from human values but decreased slightly in higher weight groups. Left ventricular diastolic function (E/e′) and right ventricular systolic indices (fractional area change [FAC]) showed distinct weight-dependent patterns. Sex did not significantly affect any echocardiographic parameters.
Conclusion
Weight-associated variations reflect physiological cardiovascular development in Diannan small-ear pigs. This study provides baseline non-invasive echocardiographic data for this breed under isoflurane anesthesia. These data offer essential reference values for cardiovascular disease modeling, xenotransplant donor screening, and pre-operative assessment of novel cardiovascular technologies.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12872-025-05425-w.
Keywords: Transthoracic echocardiography, Diannan small-ear pigs, Reference ranges
Introduction
Heart failure represents the terminal stage of various cardiovascular diseases and remains one of the leading causes of morbidity and mortality worldwide [1]. Despite advances in pharmacological therapy and device-based interventions, the five-year mortality rate among patients with end-stage heart failure is still approximately 50%[2]. The development of reliable and physiologically relevant large animal models is imperative for cardiovascular research, serving as a pivotal platform to investigate disease mechanisms, evaluate new diagnostics and therapies, and advance translational medicine [3, 4].
The close similarity between pigs and humans in terms of cardiac anatomy, physiology, and electrophysiology establishes pigs as an ideal model for cardiovascular research [5–7]. Consequently, they have been widely utilized in studies involving disease modeling, imaging optimization, device validation, and regenerative medicine [8, 9]. In addition, their high reproductive efficiency, ease of husbandry, and the maturity of gene-editing technologies further strengthen their pivotal role in both basic and translational medical research [10].
Pig breeds are generally divided into farm pigs (e.g., Yorkshire, Duroc) and miniature pigs (e.g., Göttingen, Yucatan) [11]. Pigs typically exhibit limited coronary collateral circulation, making them prone to ischemia-induced arrhythmias [11]. Compared with farm pigs, miniature pigs of similar body weight exhibit more stable cardiovascular performance and better tolerance to experimental procedures, likely due to their slower growth rate and more stable physiological status at comparable body sizes [11]. Thus, breed-specific characterization of cardiac structure and function is necessary to ensure scientific validity and reliability in experimental models.
The Diannan small-ear pig is an indigenous miniature breed from Yunnan, China. This breed is characterized by small body size, a stable genetic background, and high reproductive capacity, making it well-suited for long-term maintenance in experimental settings [12]. Recently, its application has expanded in xenotransplantation, immunological studies, and human disease modeling [13]. However, systematic echocardiographic evaluation of cardiac structure and function has not yet been performed for Diannan small-ear pigs, especially using non-invasive transthoracic echocardiography (TTE). This lack of data has limited its potential utilization in disease modeling, imaging evaluation, and validation of interventional treatments.
Therefore, the aim of this study was to systematically characterize cardiac geometry and hemodynamic parameters in healthy Diannan small-ear pigs using TTE under isoflurane anesthesia. Specifically, we sought to establish baseline reference values across different body-weight stages, analyze weight-dependent variations, and compare these findings with human reference data. The findings provide essential experimental data to support the standardized use of this breed in both basic and translational cardiovascular research.
Materials and methods
A total of 31 healthy Diannan small-ear pigs (male, n = 15; female, n = 16) were included in this prospective study. The pigs were divided into three weight groups: 20–39 kg (n = 12), 40–59 kg (n = 10), and 60–80 kg (n = 9). The study protocol was approved by the Institutional Animal Care and Use Committee of Yunnan Agricultural University.
Animal instrumentation
Animals were provided by the Yunnan Provincial Key Laboratory of Miniature Pig Gene Editing and Xenograft Transplantation. All pigs were housed consistently in pens with a 12-hour light-dark cycle and provided free access to drinking water. Before the TTE examination, animals were weighed, and body length was measured from head to tail, excluding limbs. Subsequently, pigs were positioned supine and anesthetized by inhalation of isoflurane (induction concentration: 5%; maintenance concentration: 2%). Their legs were secured in an extended position, and an electrocardiogram (ECG) was attached. Body surface area (BSA) was calculated using the formulas specifically validated for miniature pigs, as described by Swindle et al.[14]: BSA (m2) = 0.121 × (body weight)0.575. After TTE completion, isoflurane anesthesia was discontinued. Animals were continuously monitored until full recovery of spontaneous respiration and motor function, after which they were returned to their standard housing conditions for follow-up observation.
Echocardiography
Echocardiography was performed using a GE Vivid™ iq system equipped with an M5Sc (1.5–4.6 MHz) probe (GE Vingmed Ultrasound AS, Horten, Norway). ECG-synchronized frames from at least three consecutive cardiac cycles were recorded and stored on a hard disk. Certified cardiac sonographers performed the TTE, during which blinding was not feasible due to overt size differences. All subsequent offline analyses were performed by two experienced sonographers who were blinded to weight-group allocation.
Examined sections included the parasternal long-axis (Fig. 1) and other cardiac views, including parasternal short-axis and apical four-chamber views (Fig. 2). All assessments were conducted using two-dimensional (2D) and color Doppler echocardiographic techniques. Quantification parameters from M-mode ultrasound, pulsed-wave Doppler, and tissue Doppler ultrasound were included as necessary.
Fig. 1.
Parasternal long-axis views. A Standard left parasternal window obtained at the left sternal border. B Modified right parasternal window obtained at the right sternal border. C Color Doppler flow imaging of the left ventricular long-axis view. AAO, ascending aorta; AV, aortic valve; IVS, interventricular septum; LA, left atrium; LV, left ventricle; MV, mitral valve; RV, right ventricle
Fig. 2.
Other cardiac views. A Parasternal short-axis view (level of papillary muscles) from the right sternal border. B Parasternal short-axis view from the left sternal border, focused on PV and MPA. C Apical four-chamber view from the left sternal border. APM, antero-lateral papillary muscle; AV, aortic valve; LA, left atrium; LV, left ventricle; MPA, main pulmonary artery; MV, mitral valve; PPM, postero-medial papillary muscle; PV, pulmonary valve; RA, right atrium; RV, right ventricle; TV, tricuspid valve
Cardiac measurements were obtained from standardized TTE views. In the parasternal long-axis view, M-mode imaging was used to measure right ventricular anteroposterior dimension, left ventricular diameters, interventricular septal thickness, posterior wall thickness, and to calculate left ventricular ejection fraction (LVEF) using the Teichholz method. The anteroposterior diameter of the left atrium was measured at end-systole. 2D still frames at end-diastole were used to measure the diameters of the aortic annulus, sinus of Valsalva, sinotubular junction, and proximal ascending aorta. In the parasternal short-axis view at the level of the great vessels, the main pulmonary artery diameter was measured 1 cm distal to the pulmonary valve annulus at end-diastole. Pulmonary valve flow velocity was assessed using pulsed-wave Doppler. In the apical four-chamber view, 2D imaging was used to measure basal, middle, and longitudinal dimensions of the right ventricle at end-diastole, and longitudinal and transverse diameters of both left and right atria at end-systole. Hemodynamic assessments of the aortic, mitral, and tricuspid valves, along with the left ventricular outflow tract (LVOT), were performed using pulsed-wave Doppler as appropriate. Early diastolic mitral inflow velocity (E) was measured using pulsed-wave Doppler, and early diastolic mitral annular velocities (e′) at the septal and lateral annuli were measured using tissue Doppler imaging. Their mean value was calculated to determine the E/e′ratio, estimating left ventricular diastolic function.
TTE image quality was assessed and graded as follows:
Good: Standard left parasternal long-axis view (obtained from the left parasternal window) and modified right parasternal long-axis view (obtained from the right parasternal window) provided clear visualization and easy identification of cardiac structures.
Sufficient: Parasternal short-axis view at the papillary muscle level (obtained from the right sternal border) and parasternal short-axis view focused on the pulmonary valve and main pulmonary artery (obtained from the left sternal border) allowed adequate visualization of structures for evaluation.
Poor: Apical views (including four-chamber, two-chamber, and long-axis views) acquired from the left sternal border adjacent to the xiphoid process showed partially limited structural visualization due to anatomical constraints.
Human reference data
Reference values for human echocardiographic parameters were obtained from a large, nationwide, population-based study of healthy Han Chinese adults (N = 1394; male, n = 678; age range: 18–79 years; mean age: 47.3 ± 16.0 years; weight: 67.6 ± 7.9 kg), conducted across 43 echocardiographic laboratories in China. Participants were volunteers confirmed to be free of cardiovascular disease through screening [15]. Cardiac chamber dimensions and great arterial diameters were measured using standard M-mode and 2D TTE, according to the American Society of Echocardiography guidelines [16].
In the present study, a subset of reference values (mean ± standard deviation [SD]) from this cohort was used for comparative analysis. Parameters compared included left ventricular diameters, volumes, wall thickness, mass, LVEF, left and right atrial diameters and volumes, and diameters of the aortic root and main pulmonary artery.
Statistical analysis
Data collection and statistical analyses were performed using SPSS Statistics version 26 (IBM, Armonk, NY, USA), Python, and GraphPad Prism version 9.0.0 (GraphPad Software, San Diego, CA, USA). Normality was assessed using the Shapiro-Wilk test. Normally distributed variables are presented as mean ± SD, whereas non-normally distributed variables are expressed as median [interquartile range (IQR)]. For normally distributed data, differences between two groups were evaluated using the independent-samples t-test, and comparisons among multiple groups were performed using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test. For non-normally distributed data, the Mann–Whitney U test was applied for two-group comparisons, while the Kruskal–Wallis test followed by Dunn’s post hoc test was used for comparisons among three groups. Selected study parameters were compared with standard reference values for healthy Han Chinese adults using Welch’s t-test when the assumption of equal variances was not met. The relationship between body weight and cardiac structural parameters was evaluated using simple linear regression analysis. A P-value < 0.05 was considered statistically significant.
Result
The baseline data
All 31 Diannan small-ear pigs completed the study. The mean body weight was 47.2 ± 17.2 kg (range: 22–79.5 kg). Mild mitral regurgitation was detected in two pigs (6.5%) during echocardiographic screening. No other structural or hemodynamic abnormalities were observed. Signalment, age, body weight (used to calculate body surface area) and heart rate were recorded at the beginning of the echocardiographic examination (Table 1). No significant differences in body weight, body surface area, or heart rate were found between males and females (P > 0.05). In contrast, heart rate varied significantly among body weight groups, lighter pigs exhibited higher rates, but heart rate stabilized once body weight exceeded 40 kg.
Table 1.
Baseline characteristics of Diannan small-ear pigs
| Gender | Body weight groups (kg) | |||||||
|---|---|---|---|---|---|---|---|---|
| Items | Total (n = 31) | Male (n = 15) | Female (n = 16) | P value | 20–39 (n = 12) | 40–59 (n = 10) | 60–80 (n = 9) | P value |
| Age (month) | 14.5 ± 5.0 | 16.1 ± 5.1 | 13.1 ± 4.3 | 0.105 | 9.3 ± 1.8 | 15.6 ± 1.7* | 20.44 ± 1.9*+ | < 0.001 |
| Body Weight (kg) | 47.2 ± 17.2 | 47.9 ± 17.6 | 46.5 ± 16.2 | 0.824 | 29.3 ± 4.0 | 49.2 ± 5.5* | 68.8 ± 6.0*+ | < 0.001 |
| Body surface area (m2 ) | 1.1 ± 0.2 | 1.1 ± 0.2 | 1.1 ± 0.2 | 0.837 | 0.8 ± 0.1 | 1.1 ± 0.1* | 1.4 ± 0.1*+ | < 0.001 |
| Gender (male/female) | 6/6 | 4/6 | 5/4 | 0.787 | ||||
| Heart rate (bpm/min) | 157.4 ± 30.4 | 159.5 ± 26.1 | 155.4 ± 33.9 | 0.715 | 183.7 ± 16.0 | 140.8 ± 24.5* | 140.8 ± 26.2* | < 0.001 |
| Duration time of the echocardiography (min) | 19.0 ± 3.3 | 18.8 ± 3.8 | 19.1 ± 2.5 | 0.787 | 16.2 ± 2.0 | 20.3 ± 2.3* | 21.2 ± 2.7* | < 0.001 |
Data are expressed as mean ± SD, or n
*P < 0.05 versus pigs weighted 20–39 kg, +P < 0.05 versus pigs weighted 40–59 kg
Left ventricle
Summary data for left ventricular dimensions and functional parameters are presented in Table 2. Compared with published reference values in healthy Han Chinese adults [15], Diannan small-ear pigs exhibited significantly smaller left ventricular end-diastolic diameter (LVEDD), end-systolic diameter (LVESD), end-diastolic volume (LVEDV), end-systolic volume (LVESV), and left ventricular mass (LVM) (all P < 0.05). In contrast, interventricular septal thickness at end-diastole (IVSd) and left ventricular posterior wall thickness at end-diastole (LVPWd) were significantly greater in pigs than in the human reference population (P < 0.05). No significant difference in LVEF was observed between the two species (P > 0.05).
Table 2.
Left ventricular dimensions and function in Diannan small-ear pigs vs. human reference
| Gender | Body weight groups (kg) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Parameter | Total (n = 31) | Human Reference (n = 678) | P value | Male (n = 15) | Female (n = 16) | P value | 20–39 (n = 12) | 40–59 (n = 10) | 60–80 (n = 9) | P value |
| LVEDD (mm) | 33.9 ± 4.5 | 46.2 ± 4.0 | < 0.001 | 33.5 ± 4.6 | 34.3 ± 4.4 | 0.644 | 29.6 ± 2.9 | 34.8 ± 1.8* | 38.6 ± 2.8*+ | < 0.001 |
| LVESD (mm) | 22.2 ± 3.4 | 30.6 ± 4.1 | < 0.001 | 21.5 ± 3.2 | 22.8 ± 3.4 | 0.280 | 18.9 ± 1.4 | 22.7 ± 1.7* | 25.9 ± 2.2*+ | < 0.001 |
| LVEDV (ml) | 48.8 ± 15.8 | 86.7 ± 20.8 | < 0.0001 | 48.2 ± 16.9 | 49.5 ± 14.6 | 0.825 | 34.8 ± 8.7 | 50.2 ± 6.3* | 66.0 ± 12.4*+ | < 0.001 |
| LVESV (ml) | 17.2 ± 6.5 | 31.2 ± 9.6 | < 0.0001 | 16.0 ± 5.8 | 18.2 ± 6.9 | 0.366 | 11.1 ± 1.7 | 17.6 ± 3.3* | 24.8 ± 4.6*+ | < 0.001 |
| SV (ml) | 31.4 ± 10.4 | 31.5 ± 12.0 | 31.2 ± 8.8 | 0.945 | 23.2 ± 7.2 | 32.4 ± 4.7* | 41.2 ± 9.7*+ | < 0.001 | ||
| LVFS (%) | 33.9 ± 4.6 | 34.2 ± 5.1 | 33.6 ± 4.0 | 0.736 | 35.8 ± 3.1 | 32.5 ± 6.0 | 32.9 ± 3.2 | 0.182 | ||
| LVEF (%) | 64.8 ± 4.4 | 64.4 ± 6.0 | 0.588 | 66.1 ± 2.9 | 63.6 ± 5.2 | 0.114 | 67.0 ± 3.7 | 64.6 ± 3.9 | 62.1 ± 4.4* | 0.042 |
| LVM (g) | 93.2 ± 32.0 | 135.8 ± 29.7 | < 0.0001 | 93.6 ± 32.7 | 92.9 ± 31.4 | 0.952 | 61.1 ± 11.2 | 98.1 ± 11.0* | 130.6 ± 20.6*+ | < 0.001 |
| IVSd (mm) | 9.5 ± 1.2 | 8.9 ± 1.3 | 0.011 | 9.8 ± 1.2 | 9.2 ± 1.1 | 0.171 | 8.3 ± 0.7 | 9.7 ± 0.6* | 10.8 ± 0.6*+ | < 0.001 |
| IVSs (mm) | 11.9 ± 1.7 | 12.5 ± 1.8 | 0.049 | 11.867 ± 1.8 | 11.7 ± 1.7 | 0.754 | 10.2 ± 1.3 | 12.3 ± 1.00* | 13.3 ± 0.9* | < 0.001 |
| LVPWd (mm) | 9.3 ± 1.1 | 8.7 ± 1.2 | 0.021 | 9.267 ± 1.2 | 9.250 ± 1.0 | 0.968 | 8.2 ± 0.6 | 9.7 ± 0.6* | 10.2 ± 0.8* | < 0.001 |
| LVPWs (mm) | 12(11–13) | 12.5 ± 1.9 | 0.337 | 11(11–13) | 12(11–13) | 0.779 | 11(10–11) | 12(12–14)* | 14(12–16)* | 0.001 |
| E-MV (cm/s) | 93.3 ± 17.4 | 97.3 ± 17.7 | 89.6 ± 16.2 | 0.226 | 94.8 ± 12.3 | 94.2 ± 11.9 | 90.4 ± 25.8 | 0.851 | ||
| septal e′ (cm/s) | 9(8–10) | 9(9–11) | 9(8–10) | 0.089 | 9(8–9) | 9(8–9) | 11(8–11) | 0.240 | ||
| lateral e′ (cm/s) | 10(9–12) | 11(10–12) | 10(9–12) | 0.472 | 10(9–10) | 11(9–12) | 12(10–18)* | 0.020 | ||
| E/e′ (ratio) | 9.8(8.4–10.3) | 10.2(9.3–10.3) | 9.7(7.7–10.2) | 0.767 | 10.3(10.2–10.5) | 9.6(9.3–10.3) | 7.2(6.5–7.7)*+ | < 0.001 | ||
Abbreviation: E-MV mitral early-diastolic inflow peak velocity, IVSd interventricular septum end-diathickness, IVSs interventricular septum end-systolic thickness, LA area, left atrial area, LVEDD leftventricular end-diastolic diameter, LVEDV left ventricular end-diastolic volume, LVEF left ventriculejection fraction, LVESD left ventricular end-systolic diameter, LVESV left ventricular end-systolicvolume, LVFS left ventricular fractional shortening, LVM left ventricular mass, LVPWd left ventricuposterior wall end-diastolic thickness, LVPWs left ventricular posterior wall end-systolic thickness, area, right atrial area, SV stroke volume
Values are expressed as mean ± SD, or median (interquartile range, IQR)
*P < 0.05 versus pigs weighted 20–39 kg, +P < 0.05 versus pigs weighted 40–59 kg
Across pig body weight groups, no significant differences were noted in LV fractional shortening (LVFS), early mitral inflow velocity (E-MV), or septal e′ (P > 0.05). However, increasing body weight was associated with significant progressive increases in LVEDD, LVESD, LVEDV, LVESV, stroke volume (SV), LVM, IVSd, IVSs, LVPWd, LVPWs, and lateral e′ (all P < 0.05). Conversely, LVEF and E/e′ ratio decreased significantly with increasing body weight (P < 0.05). No sex-related differences were observed for left ventricular parameters (P > 0.05).
Left and right Atria
Atrial structural parameters of Diannan small-ear pigs are presented in Table 3. Compared with healthy adult humans in China [15], both atrial diameters and areas were smaller in this breed, with no significant differences between sexes (P > 0.05). With increasing body weight, the anteroposterior, transverse, and longitudinal diameters and area of the left atrium, as well as transverse and longitudinal diameters and area of the right atrium, progressively increased (P < 0.05).
Table 3.
Atrial dimensions in Diannan small-ear pigs vs. human reference
| Gender | Body weight groups (kg) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Parameter | Total (n = 31) | Human Reference (n = 678) | P value | Male (n = 15) | Female(n = 16) | P value | 20–39 (n = 12) | 40–59 (n = 10) | 60–80 (n = 9) | P value |
| Left atrium | ||||||||||
| LA-ap (mm) | 22(21–23) | 31.1 ± 3.9 | < 0.0001 | 21(21–22) | 22(21–23) | 0.533 | 21 (20–22) | 21(20–22) | 23(22–25)*+ | 0.010 |
| LA-t (mm) | 26.0 ± 4.0 | 35.7 ± 4.6 | < 0.0001 | 26.2 ± 4.4 | 25.8 ± 3.6 | 0.796 | 23.8 ± 2.6 | 25.0 ± 2.3 | 30.11 ± 3.9*+ | < 0.001 |
| LA-l (mm) | 40.3 ± 6.5 | 46.8 ± 5.9 | < 0.0001 | 40.1 ± 4.7 | 40.4 ± 7.7 | 0.92 | 35.6 ± 2.8 | 39.0 ± 1.7 | 47.9 ± 6.4*+ | < 0.001 |
| LA area (cm2) | 8.4 ± 1.7 | 14.7 ± 3.2 | < 0.0001 | 8.5 ± 1.7 | 8.3 ± 1.6 | 0.708 | 6.8 ± 0.7 | 8.5 ± 0.4* | 10.3 ± 1.1*+ | < 0.001 |
| Right atrium | ||||||||||
| RA-t (mm) | 20.5 ± 4.4 | 35.4 ± 4.6 | < 0.0001 | 20.8 ± 4.7 | 20.6 ± 4.1 | 0.916 | 17.1 ± 1.9 | 20.6 ± 2.7)* | 25.7 ± 3.6*+ | < 0.001 |
| RA-l (mm) | 38.3 ± 5.4 | 44.4 ± 4.7 | < 0.0001 | 39.7 ± 5.2 | 37.8 ± 5.6 | 0.346 | 34.5 ± 2.8 | 37.4 ± 1.9 | 45.9 ± 3.4*+ | < 0.001 |
| RA area (cm2) | 7.7 ± 1.5 | 7.8 ± 1.5 | 7.7 ± 1.5 | 0.739 | 6.2 ± 1.0 | 8.1 ± 0.6* | 9.4 ± 0.6*+ | < 0.001 | ||
Abbreviation: LA-ap left atrial anteroposterior dimension, LA-l left atrial long-axis dimension, LA-t left atrial transverse dimension, RA-l right atrial long-axis dimension, RA-t right atrial transverse dimension
Values are expressed as mean ± SD
*P < 0.05 versus pigs weighted 20–39 kg, +P < 0.05 versus pigs weighted 40–59 kg
*P < 0.05 versus pigs weighted 20–39 kg, +P < 0.05 versus pigs weighted 40–59 kg
Right ventricle
Right ventricular (RV) dimensions and functional parameters of Diannan small-ear pigs are summarized in Table 4. RV diameter increased progressively with body weight but remained below the human reference range [15] (all P < 0.05). No significant sex-related differences were found (all P > 0.05). Among RV functional parameters, FAC increased significantly with greater body weight (P < 0.05). TAPSE and early diastolic tricuspid inflow velocity (E-TV) did not differ significantly among body weight groups (P > 0.05).
Table 4.
Right ventricular dimensions and function in Diannan small-ear pigs vs. human reference
| Gender | Body weight groups (kg) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Total(n = 31) | Human Reference (n = 678) | P value | Male (n = 15) | Female (n = 16) | P value | 20–39 (n = 12) | 40–59 (n = 10) | 60–80 (n = 9) | P value | |
| RV dimensions | ||||||||||
| anteroposterior dimension (mm) | 14.7 ± 1.9 | 22.3 ± 3.9 | < 0.0001 | 14.5 ± 1.5 | 15.0 ± 2.2 | 0.448 | 13.1 ± 1.2 | 15.2 ± 1.0* | 16.4 ± 1.6* | < 0.001 |
| basal dimension (mm) | 20.2 ± 3.2 | 32.2 ± 5.1 | < 0.0001 | 19.9 ± 2.8 | 20.6 ± 3.5 | 0.561 | 18.2 ± 2.3 | 19.8 ± 1.8 | 23.4 ± 2.9*+ | < 0.001 |
| middile dimension (mm) | 16.0 ± 2.6 | 26.7 ± 5.2 | < 0.0001 | 15.3 ± 2.3 | 16.6 ± 2.7 | 0.200 | 13.8 ± 1.4 | 18.3 ± 1.7* | 16.3 ± 2.2* | < 0.001 |
| long-axis dimension (mm) | 38.0 ± 7.1 | 56.1 ± 9.7 | < 0.0001 | 38.1 ± 7.6 | 37.9 ± 6.7 | 0.923 | 32.3 ± 5.0 | 39.0 ± 2.2* | 44.4 ± 7.1* | < 0.001 |
| TAPSE (mm) | 44.8 ± 1.6 | 44.8 ± 1.9 | 44.9 ± 1.2 | 0.900 | 44.1 ± 1.2 | 45.4 ± 1.3 | 45.2 ± 1.9 | 0.112 | ||
| FAC (%) | 14.8 ± 1.7 | 15.4 ± 1.7 | 14.3 ± 1.6 | 0.068 | 13.5 ± 1.4 | 15.2 ± 1.0* | 16.1 ± 1.6* | < 0.001 | ||
| E-TV (cm/s) | 88.4 ± 15.2 | 85.9 ± 15.8 | 90.7 ± 14.2 | 0.395 | 91.2 ± 3.7 | 90.6 ± 7.2 | 82.1 ± 20.8 | 0.366 | ||
Abbreviation: E-TV, tricuspid valve early-diastolic inflow peak velocity; FAC, fractional areashortening; RV, right ventricular; TAPSE, tricuspid annular plane systolic excursion.
Values are expressed as mean ± SD
Aortic and pulmonary artery
Diameters of the aorta and pulmonary artery in Diannan small-ear pigs were significantly smaller than established normal reference values for humans [15] (P < 0.05), with no statistically significant differences between sexes (P > 0.05). Across body weight groups, diameters of the annulus, sinus, sinotubular junction, and main pulmonary artery increased significantly with body weight (all P < 0.01). Specifically, values in the 60–80 kg group were significantly greater than those in both the 20–39 kg and 40–59 kg groups (P < 0.05) (Table 5).
Table 5.
The aortic and pulmonary artery dimensions in Diannan small-ear pigs vs. human reference
| Gender | Body weight groups (kg) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Parameter | Total (n = 31) | Human Reference (n = 678) | P value | Male (n = 15) | Female(n = 16) | P value | 20–39 (n = 12) | 40–59 (n = 10) | 60–80 (n = 9) | P value |
| Aortic diameter | ||||||||||
| annular (mm) | 17.0 ± 1.7 | 21.3 ± 2.5 | < 0.0001 | 17.3 ± 1.7 | 16.8 ± 1.7 | 0.365 | 16.9 ± 1.1 | 15.7 ± 0.3 | 18.7 ± 1.4*+ | < 0.001 |
| sinus (mm) | 23.8 ± 2.1 | 30.1 ± 3.2 | < 0.0001 | 23.8 ± 1.7 | 23.8 ± 2.5 | 0.950 | 22.8 ± 1.5 | 23.1 ± 1.7 | 25.9 ± 1.8*+ | < 0.001 |
| sinotubular junction (mm) | 18(17–19) | 22–36 | < 0.001 | 18(17–19) | 18(17–19) | 0.840 | 18(17–18) | 16(16–18) | 20(19–21)*+ | 0.002 |
| proximal ascending aortic (mm) | 19.2 ± 2.1 | 27.7 ± 3.7 | < 0.0001 | 19.0 ± 1.8 | 19.5 ± 2.4 | 0.532 | 18.8 ± 1.7 | 18.6 ± 1.9 | 20.7 ± 2.3 | 0.064 |
| Pulmonary artery diameter | ||||||||||
| main pulmonary artery (mm) | 14.6 ± 1.9 | 20.7 ± 2.8 | < 0.001 | 14.8 ± 2.0 | 14.5 ± 1.8 | 0.677 | 12.9 ± 0.9 | 14.8 ± 1.2* | 16.8 ± 1.1*+ | < 0.001 |
| Peak velocity | ||||||||||
| LVOT-v (cm/s) | 95.9 ± 16.3 | 94.5 ± 15.2 | 97.3 ± 17.2 | 0.649 | 104.1 ± 17.1 | 90.4 ± 8.4 | 91.3 ± 17.6 | 0.092 | ||
| AV-v (cm/s) | 105.9 ± 18.6 | 104.0 ± 22.5 | 107.6 ± 13.8 | 0.603 | 113.8 ± 14.1 | 106.6 ± 14.5 | 94.4 ± 22.0 | 0.062 | ||
| PV-v (cm/s) | 105.0 ± 16.7 | 105.6 ± 19.2 | 104.6 ± 13.8 | 0.893 | 112.3 ± 17.9 | 102.1 ± 14.9 | 98. 6 ± 12.8 | 0.147 | ||
Abbreviation: AV-v peak systolic aortic valve flow rate, LVOT-v peak systolic flow rate of the leftventricular outflow tract, PV-v peak systolic velocity of the pulmonary valve
Values are expressed as mean ± SD, or median (IQR)
*P < 0.05 versus pigs weighted 20–39 kg, +P < 0.05 versus pigs weighted 40–59 kg
Body weight–dependent changes in cardiac structural parameters
Linear regression analysis demonstrated strong positive correlations between body weight and key cardiac structural parameters (Fig. 3). Left ventricular dimensions (LVEDD, LVESD), volumes (LVEDV, LVESV), mass (LVM), atrial sizes (LA area, RA area, RA-l), and main pulmonary artery diameter increased significantly with increasing body weight (all R² > 0.7, P < 0.0001), indicating consistent weight-dependent structural growth. Comparisons across body weight groups (Fig. 4) further highlighted these trends. Representative parameters—including left ventricular dimensions and wall thickness (LVEDD, LVEDV, LVM, IVSd, LVPWd), atrial areas, and great vessel diameters (aortic sinus, main pulmonary artery)—progressively increased with higher body weight, with the largest values observed in the 60–80 kg group, reflecting stage-dependent morphological adaptation in Diannan small-ear pigs.
Fig. 3.
Linear regression analysis between body weight and key cardiac structural parameters. Scatter plots with fitted regression lines illustrate the positive associations between body weight and representative echocardiographic indices: A LVEDD, B LVESD, C LVEDV, D LVESV, E LVM, F LA area, G RA area, H RA-l, and I main pulmonary artery diameter. All correlations were significant (R² > 0.7, P < 0.0001), demonstrating consistent weight-dependent structural growth
Fig. 4.
Comparison of key echocardiographic parameters among different body weight groups. Bar graphs show progressive increases in representative structural indices across body weight categories (Group 1: 20–39 kg; Group 2: 40–59 kg; and Group 3: 60–80 kg). Panels (A–I) correspond to LVEDD, LVEDV, LVM, IVSd, LVPWd, LA area, RA area, aortic sinus diameter, and main pulmonary artery diameter, respectively. Data are presented as mean ± SD, *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, ns indicates no statistically significant difference between groups
BSA-indexed structural parameters
Cardiac structural parameters indexed to BSA showed significant differences across body weight groups (Supplementary Table S1). With increasing body weight, left ventricular dimensions (LVEDD and LVESD) decreased significantly (P < 0.001), whereas LVM increased (P < 0.001). Wall thickness parameters (IVSd and LVPWd) were highest in the 20–39 kg group and declined significantly with increasing weight (P < 0.001), reflecting a “small-cavity, thick-wall” phenotypic pattern. Both atrial dimensions and right ventricular diameters also decreased with body weight (P < 0.001). Similarly, great vessel parameters—including aortic annulus, sinus, sinotubular junction, proximal ascending aorta, and main pulmonary artery diameters—were significantly smaller in higher weight groups (P < 0.001). Overall, BSA-indexed cardiac structural parameters exhibited systematic variation with body weight, indicating weight-dependent proportional remodeling in Diannan small-ear pigs.
Discussion
This study established baseline reference values for noninvasive TTE in healthy Diannan small-ear pigs under isoflurane anesthesia. Cardiac geometry and functional parameters were systematically characterized. The main findings were as follows: (1) Structural indices of ventricles, atria, and great vessels increased with body weight and stabilized beyond 40 kg, indicating distinct developmental stages; (2) Compared with healthy adult humans in China, this breed had smaller cardiac chambers and vascular dimensions but greater myocardial thickness, reflecting a species-specific “small chamber–thick wall” phenotype; (3) Sex did not significantly affect cardiac measurements, while body weight substantially influenced multiple functional indices. These findings collectively support the suitability of the Diannan small-ear pig as a large-animal model for cardiovascular research.
Due to quadrupedal posture and thoracic conformation, porcine hearts are oriented differently from human hearts. The long axis is cranially inclined and rotated leftward, with the left heart system positioned caudally and the right heart system cranially [11]. Additionally, the patterns of caval venous inflow and number of pulmonary veins differ from humans. These anatomical characteristics affect acoustic window selection for TTE and may cause shifts in anatomical landmarks on ultrasound images. Such differences represent fundamental structural variations relevant to model use and image interpretation.
Previous studies have predominantly used TEE as the primary imaging method, particularly for intraoperative monitoring. For example, several investigators have employed TEE to establish standard imaging planes and measurement parameters in porcine hearts [17, 18], sometimes combined with pressure–strain loop analysis to assess myocardial work [19]. Other studies have utilized epicardial echocardiography before left ventricular assist device implantation to acquire comprehensive cardiac parameters [20, 21]. However, the semi-invasive nature of TEE limits its applicability for preoperative screening and long-term animal follow-up.
In the present study, noninvasive TTE was used to obtain baseline cardiac parameters in Diannan small-ear pigs. Probe placement generally aligned with previous reports [22]. Technical challenges occurred when acquiring standard apical four-chamber views due to the sagittal protrusion of the sternum and narrow intercostal spaces [19, 23]. The porcine heart is centrally located in the thoracic cavity, and its long axis is perpendicular to the body axis [24]. The cardiac apex typically projects toward the left sixth or seventh intercostal space [25]. This anatomical arrangement results in an inherent oblique angle between the interventricular septum and ultrasound beam in apical or subxiphoid four-chamber views, causing lateral image deviation. Artificial probe adjustment to center the septum in the imaging plane may deviate from standard planes, introducing measurement errors through ventricular foreshortening.
To overcome imaging limitations imposed by the thoracic conformation of small pigs, the acquisition protocol for acquiring the parasternal long-axis view from the left sternal border was optimized. Left ventricular geometric and functional parameters were measured from a long-axis view at the right sternal border, aligned closely with the ventricular long axis to minimize foreshortening artifacts. In contrast, great vessel measurements were acquired from the left sternal border to enhance image quality and measurement reproducibility. This noninvasive and reproducible technical approach provides a practical assessment tool for cardiovascular research using Diannan small-ear pigs.
This study identified no sex-related differences in echocardiographic parameters of Diannan small-ear pigs. Most parameters correlated with body weight, consistent with findings reported in domestic and miniature pig breeds [26]. Previous studies reported that porcine hearts generally have a more robust overall structure than human hearts, often exhibiting thicker ventricular walls and larger chambers [20]. In Polish Landrace pigs, left ventricular diameter and wall thickness increase significantly with body weight, while the correlation between certain functional indices (such as LVEF) and body weight diminishes in heavier animals (> 70 kg) [26]. Cardiac MRI studies in German Landrace pigs have reported LVEDD of approximately 50–52 mm and wall thicknesses of 5–6 mm[27].
In comparison, Diannan small-ear pigs within a similar body weight range exhibit smaller left ventricular cavities but relatively thicker ventricular walls, suggesting the presence of mild physiological myocardial hypertrophy. When compared with other miniature pig breeds, such as Göttingen minipigs, the structural parameters of Diannan small-ear pigs are generally comparable. Previous reports have shown that Göttingen minipigs have a LVEDV of approximately 35–40 ml and wall thicknesses typically below 10 mm[28]. In the present study, the LVEDV of Diannan small-ear pigs was 48.8 ± 15.8 ml, with IVSd and LVPWd of 9.5 ± 1.2 mm and 9.3 ± 1.1 mm, respectively—values close to those of Göttingen minipigs. Overall, while absolute cardiac chamber dimensions increased with body weight in Diannan small-ear pigs, BSA-indexed parameters revealed a distinct pattern of proportionally smaller chambers with relatively thicker walls. This “small-cavity, thick-wall” phenotype reflects an adaptive structural remodeling likely associated with breed-specific traits and body conformation, rather than pathological change. This unique anatomical profile should be taken into consideration when utilizing this breed for disease modeling, device testing, or translational applications.
Additionally, Diannan small-ear pigs have a relatively high baseline heart rate, which remains elevated even under isoflurane anesthesia. This significantly shortens the diastolic phase, limiting ventricular filling and consequently resulting in smaller left ventricular end-diastolic diameters. According to the Law of Laplace, a smaller ventricular radius combined with thickened ventricular walls effectively reduces wall stress, partially offsetting the adverse effects of decreased preload on myocardial contractility and maintaining LVEF within normal range [29, 30]. This compensatory mechanism is more pronounced in heavier individuals, suggesting that the cardiovascular system of Diannan small-ear pigs gradually develops adaptive capacity to hemodynamic load changes during growth.
This study also observed significantly smaller diameters of the aorta and pulmonary artery compared with established human reference values. Therefore, careful consideration of vascular diameter and device compatibility is essential prior to experimental procedures such as transcatheter valve replacement, aortic reconstruction, or xenotransplantation. These baseline data provide important references for future interventional operations, help optimize the selection and utilization of experimental animals, and contribute to reducing resource waste.
Several limitations should be considered in this study. First, although the animals were grouped by body weight, the relatively wide weight range within groups and the limited overall sample size may reduce the statistical power and generalizability of the findings. Second, the mean age of the animals differed somewhat among groups, and age-related physiological changes—such as alterations in myocardial compliance, heart rate regulation, and hemodynamic status—may have influenced certain parameters. Furthermore, inhalation anesthesia can alter cardiac output, blood pressure, electrophysiological rhythm, and coronary perfusion [31]. As invasive blood pressure and continuous heart rate monitoring were not performed in this study, it was difficult to fully evaluate the depth of anesthesia and its impact on echocardiographic measurements. Future studies should aim to enroll larger sample sizes with more balanced distributions of body weight and age, and incorporate multi-parametric monitoring under anesthesia to enable more comprehensive cardiac functional assessment.
Conclusions
This study established a baseline TTE dataset for healthy Diannan small-ear pigs under isoflurane anesthesia, providing a reference for assessing cardiac structure and function. By tailoring probe positioning and refining measurement parameters based on anatomical characteristics specific to this breed, reliable visualization of cardiac chambers in standard imaging planes was achieved. No significant sex-related differences were observed in echocardiographic parameters, while most structural indices positively correlated with body weight. This breed exhibits a distinctive “small-cavity, thick-wall” phenotype, characterized by smaller ventricular dimensions with relatively thicker walls compared to large domestic pigs, while maintaining structural similarity to other miniature pig breeds. The resulting dataset provides essential reference values to support standardized application and translational research using this animal model in cardiovascular studies.
Supplementary Information
Acknowledgements
Not applicable.
Authors’ contributions
All authors contributed to the study’s conception and design. YD and QW proposed the conceptual design of the article. LZ and JL performed an echocardiography examination for the pigs, performed the statistical analysis, and drafted the manuscript. KL and PX were responsible for image analysis and data measurement. TW was responsible for animal anesthesia. All the authors read and approved the final manuscript.
Funding
This study was supported by the kunming Health Commission Grant (Grant Numbers: 2025-09-02-015) and Clinical medical Research Center for Cardiovascular disease of Yunnan Province (Grant Numbers: 202405AJ310005).
Data availability
The datasets that support the findings of this study are available from the corresponding author, [YD], upon reasonable request.
Declarations
Ethics approval and consent to participate
Ethical approval for this study was given by the Medical Ethics Committee of Yunnan Agricultural University (Ethics approval Number 202008003).
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Li Zhao and Jianhua Li contributed equally to this work.
Contributor Information
Yunchuan Ding, Email: dd82109@163.com.
Qinghui Wang, Email: wqh962099@163.com.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The datasets that support the findings of this study are available from the corresponding author, [YD], upon reasonable request.