Table 2.
Hemodynamic responses during a progressive ramp and step lower body negative pressure (LBNP) protocols to presyncope
| LBNP stage (mmHg) |
P values |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 15 | 30 | 45 | 60 | LBNP | Protocol | Interaction | PS 1-min | P Value | |
| SAP, mmHg | ||||||||||
| Ramp | 128.5 ± 1.9 | 127.5 ± 2.6 | 122.8 ± 1.6* | 116.8 ± 1.8* | 111.7 ± 3.3* | <0.0001 | 0.01 | 0.95 | 95.7 ± 1.4 | 0.51 |
| Step | 125.4 ± 1.8 | 124.8 ± 1.8 | 119.2 ± 2.1* | 115.6 ± 1.9* | 109.2 ± 2.1* | 94.9 ± 1.3 | ||||
| SAP, %Δ | ||||||||||
| Ramp | – | −0.8 ± 1.2 | −4.3 ± 1.0* | −9.8 ± 1.2* | −13.2 ± 2.2* | <0.0001 | 0.50 | 0.79 | −25.2 ± 1.6 | 0.31 |
| Step | – | −0.4 ± 1.1 | −4.9 ± 1.4* | −8.0 ± 1.7* | −12.7 ± 1.8* | −24.0 ± 1.7 | ||||
| DAP, mmHg | ||||||||||
| Ramp | 73.8 ± 1.3 | 73.7 ± 1.5 | 75.1 ± 1.5 | 74.2 ± 1.7 | 75.3 ± 2.7 | 0.66 | 0.06 | 0.58 | 65.0 ± 1.4 | 0.56 |
| Step | 71.8 ± 1.3 | 72.7 ± 1.3 | 72.8 ± 1.5 | 74.6 ± 1.1 | 74.8 ± 1.5 | 65.7 ± 1.4 | ||||
| DAP, %Δ | ||||||||||
| Ramp | – | −0.1 ± 1.0 | 1.8 ± 1.1 | −0.5 ± 1.2† | 1.4 ± 2.1 | 0.30 | 0.04 | 0.16 | −11.7 ± 1.6 | 0.06 |
| Step | – | 1.3 ± 0.9 | 1.4 ± 1.3 | 3.2 ± 1.4 | 2.4 ± 1.7 | −8.2 ± 2.2 | ||||
| HR, beats/min | ||||||||||
| Ramp | 59.9 ± 1.5 | 61.5 ± 1.7 | 69.1 ± 2.1* | 79.0 ± 2.4* | 86.6 ± 3.0* | <0.0001 | <0.0001 | 0.95 | 107.2 ± 5.4 | 0.31 |
| Step | 62.4 ± 1.8 | 65.6 ± 2.2 | 73.5 ± 2.8* | 83.4 ± 3.5* | 91.3 ± 3.1* | 111.0 ± 4.7 | ||||
| MAP, mmHg | ||||||||||
| Ramp | 95.4 ± 1.6 | 94.7 ± 1.8 | 93.5 ± 1.5 | 90.5 ± 1.7* | 89.4 ± 2.9* | <0.0001 | 0.02 | 0.77 | 76.1 ± 1.3 | 0.81 |
| Step | 92.8 ± 1.6 | 92.9 ± 1.6 | 90.9 ± 1.8 | 90.4 ± 1.3 | 87.9 ± 1.5* | 76.4 ± 1.3 | ||||
| SV, mL | ||||||||||
| Ramp | 99.3 ± 4.2 | 93.3 ± 3.8 | 79.8 ± 3.0* | 66.0 ± 2.8* | 55.3 ± 2.9* | <0.0001 | 0.15 | 0.98 | 47.4 ± 3.2 | 0.32 |
| Step | 98.6 ± 3.6 | 90.7 ± 3.3* | 78.0 ± 3.4* | 65.0 ± 3.4* | 53.2 ± 3.4* | 45.1 ± 3.4 | ||||
| Cardiac output, L/min | ||||||||||
| Ramp | 5.9 ± 0.2 | 5.7 ± 0.2 | 5.5 ± 0.2* | 5.2 ± 0.2* | 4.8 ± 0.3* | <0.0001 | 0.01 | 0.96 | 4.8 ± 0.2 | 0.91 |
| Step | 6.1 ± 0.2 | 5.9 ± 0.2 | 5.7 ± 0.2* | 5.3 ± 0.3* | 4.8 ± 0.3* | 4.8 ± 0.3 | ||||
| Cardiac output, %Δ | ||||||||||
| Ramp | – | −3.3 ± 1.3 | −6.8 ± 1.5* | −10.0 ± 2.1* | −16.9 ± 2.8* | <0.0001 | 0.22 | 0.88 | −17.8 ± 2.3 | 0.17 |
| Step | – | −3.5 ± 1.2 | −7.5 ± 1.8* | −12.1 ± 2.4* | −19.2 ± 2.1* | −21.4 ± 2.7 | ||||
| SVR, (mmHg/L*min−1) | ||||||||||
| Ramp | 16.8 ± 0.9† | 17.2 ± 0.8 | 17.6 ± 0.8 | 18.0 ± 0.8 | 19.3 ± 1.1* | <0.0001 | 0.0004 | 0.71 | 16.4 ± 0.8 | 0.70 |
| Step | 15.8 ± 0.6 | 16.2 ± 0.7 | 16.6 ± 0.8 | 17.5 ± 0.9* | 18.9 ± 1.2* | 16.6 ± 0.8 | ||||
| SVR, %Δ | ||||||||||
| Ramp | – | 2.9 ± 1.3 | 5.7 ± 1.8 | 5.1 ± 2.5 | 13.0 ± 3.8* | <0.0001 | 0.03 | 0.38 | −1.4 ± 2.9 | 0.03 |
| Step | – | 4.0 ± 1.5 | 6.7 ± 2.3* | 10.9 ± 2.3* | 16.7 ± 3.2* | 6.9 ± 3.5 | ||||
| SmO2, % (n = 11) | ||||||||||
| Ramp | 75.0 ± 1.6 | 74.5 ± 1.7 | 72.4 ± 2.1 | 71.2 ± 2.6 | 71.3 ± 1.3 | 0.002 | 0.06 | 0.86 | 68.5 ± 2.3 | 0.75 |
| Step | 76.9 ± 1.5 | 74.8 ± 2.0 | 73.3 ± 2.1 | 73.3 ± 1.4 | 74.5 ± 1.4 | 69.4 ± 1.9 | ||||
| SmO2, %Δ (n = 11) | ||||||||||
| Ramp | – | −0.7 ± 0.6 | −3.5 ± 1.2* | −4.8 ± 1.5* | −5.6 ± 1.2* | <0.0001 | 0.04 | 0.64 | −8.9 ± 1.7 | 0.65 |
| Step | – | −3.0 ± 1.0* | −5.0 ± 1.1* | −6.2 ± 0.8* | −6.3 ± 1.4* | −9.9 ± 1.3 | ||||
| Mean MCAv, cm/s | ||||||||||
| Ramp | 64.4 ± 3.1 | 64.3 ± 3.4 | 61.8 ± 3.7 | 58.3 ± 3.6* | 56.2 ± 3.0* | <0.0001 | 0.05 | 0.90 | 45.7 ± 2.4 | 0.09 |
| Step | 64.2 ± 3.4 | 62.4 ± 3.4 | 59.7 ± 3.5 | 56.5 ± 3.2* | 52.9 ± 3.3* | 42.8 ± 2.2 | ||||
| Mean PCAv, cm/s (n = 11) | ||||||||||
| Ramp | 40.4 ± 2.0 | 40.3 ± 2.1 | 38.8 ± 2.3 | 37.9 ± 2.8 | 39.6 ± 1.6* | <0.0001 | 0.41 | 0.81 | 33.3 ± 1.7 | 0.10 |
| Step | 41.2 ± 1.8 | 39.3 ± 2.2 | 38.4 ± 2.8 | 37.5 ± 3.4* | 37.5 ± 2.2* | 30.5 ± 2.0 | ||||
| ScO2, % | ||||||||||
| Ramp | 67.7 ± 1.4 | 66.8 ± 1.5 | 66.2 ± 1.5 | 65.6 ± 1.7 | 66.1 ± 1.8 | <0.0001 | 0.003 | 0.50 | 63.0 ± 1.5 | 0.16 |
| Step | 67.5 ± 1.6 | 66.1 ± 1.8 | 64.9 ± 1.7* | 63.6 ± 2.0* | 63.7 ± 2.5* | 60.3 ± 2.4 | ||||
| Oxyhemoglobin, µM | ||||||||||
| Ramp | 34.3 ± 2.4 | 33.4 ± 2.4 | 32.9 ± 2.4 | 33.0 ± 2.7 | 34.4 ± 4.0 | 0.02 | 0.34 | 0.76 | 30.8 ± 2.3 | 0.49 |
| Step | 34.8 ± 3.0 | 33.5 ± 3.0 | 32.4 ± 2.9 | 31.9 ± 3.1 | 32.7 ± 4.4* | 29.8 ± 2.8 | ||||
| Deoxyhemoglobin, µM | ||||||||||
| Ramp | 16.0 ± 1.1 | 16.3 ± 1.1 | 16.5 ± 1.1 | 16.9 ± 1.2 | 17.1 ± 1.8 | 0.01 | 0.09 | 0.91 | 17.7 ± 1.1 | 0.36 |
| Step | 16.2 ± 1.5 | 16.5 ± 1.5 | 16.9 ± 1.5 | 17.6 ± 1.7 | 17.6 ± 2.6 | 18.2 ± 1.6 | ||||
| Respiratory rate, breaths/min | ||||||||||
| Ramp | 13 ± 1 | 12 ± 1 | 12 ± 1 | 12 ± 1 | 12 ± 1 | 0.96 | 0.19 | 0.38 | 14 ± 2 | 0.62 |
| Step | 12 ± 1 | 12 ± 1 | 12 ± 1 | 11 ± 1 | 12 ± 1 | 15 ± 2 | ||||
| etCO2, mmHg | ||||||||||
| Ramp | 41.8 ± 1.1 | 40.9 ± 1.1 | 39.2 ± 1.2 | 37.6 ± 1.6* | 38.1 ± 1.8* | <0.0001 | 0.27 | 0.46 | 30.0 ± 1.9 | 0.22 |
| Step | 42.6 ± 1.0 | 40.9 ± 1.1 | 39.1 ± 1.4 | 36.7 ± 1.9* | 34.9 ± 2.1* | 28.3 ± 1.6 | ||||
| etCO2, %Δ | ||||||||||
| Ramp | – | −2.3 ± 0.9 | −6.2 ± 1.5* | −10.0 ± 2.6* | −12.1 ± 2.6* | <0.0001 | 0.006 | 0.45 | −28.3 ± 4.0 | 0.03 |
| Step | – | −4.0 ± 1.2 | −8.6 ± 1.8* | −13.5 ± 3.3* | −18.2 ± 4.2* | −33.7 ± 3.4 | ||||
Data are presented as absolute and relative means ± SE. *P ≤ 0.09 compared with baseline within a group. †P ≤ 0.05 differences between protocols. n = number of subjects. SAP, systolic arterial pressure; DAP, diastolic arterial pressure; etCO2, end tidal carbon dioxide; MAP, mean arterial pressure; MCAv, middle cerebral artery velocity; ScO2, cerebral oxygen saturation; SmO2, muscle oxygen saturation; SV, stroke volume; SVR, systemic vascular resistance. PS-1 time point refers to the 1 min prior to presyncope.