TABLE 2.

Troubleshooting table.

Potential problem(s)	Possible source(s) and solution(s)
From the beginning of the experiment, the uncalibrated volume signal is in the normal range (in mice 4–7; in rats 5–10 RVUs), pressure signal and dP/dt is in the lower range, the heart rate is very low (see Table 1 for normal values)	The temperature of the animal may have dropped or the anesthetic is overdosed. Check the temperature of the animal and the temperature control unit; also check the depth of the anesthesia and make sure that the anesthetic was not overdosed. If so, in case of inhalation anesthesia, decrease the concentration by 1–1.5%, or for a short period, use just 100% oxygen. Make adjustments and allow 10–15 min for stabilization. In case of injectable anesthetic overdose, i.v. fluid injection and 100% oxygen can help recovery. Make sure that animals are always intubated if injectable anesthesia is performed and trachea tubes are not blocked by mucus. If so, insert a small plastic tube (P10 in mice) to the tube connected to a 10–20 ml syringe and suck out obstructing mucus
From the beginning of the experiment, pressure signal and dP/dt is low	Animal may have lost too much blood during the surgery and/or fluid via evaporation through the surgical surface. Anesthesia/analgesia may also be overdosed or not sufficient. Use battery-operated electrocautery during the surgery to minimize blood loss and always moisturize the surgical surface with physiological saline to decrease drying out and evaporation. If the blood/fluid loss is significant, slowly inject/infuse physiological saline solution into the jugular or femoral veins; in more severe cases, inject albumin- containing solution. If the abdominal cavity is intact, saline solution can also be injected i.p. Check the anesthesia/analgesia depth. Paradoxically, if animals feel pain and distress, it can also lead to hemodynamic instability; if so, adjust the drug concentrations
From the beginning of the experiment, pressure signal and dP/dt is normal, but volume signal is very low	Most likely, the catheter is not in the right position. Try to improve the volume signal by gently readjusting the position of the catheter
The pressure and/or volume signal is noisy, regular 50 Hz (Europe) to 60 Hz (USA) noise pattern	The most likely cause is electric interference, which can originate from pumps, electrocautery devices, ungrounded operating tables, ventilators/respirators, fluorescent lamps, transformers, fans and electric warming blankets. Try to isolate any sources of electrical interference by moving them away from the catheter and by sequentially unplugging the possible interfering appliances. If the noise is coming from the power supply, sometimes just unplugging the MPVS system and plugging into different outlet, preferably with stabilized power supply for the laboratory equipment, can eliminate the problem. If the noise problem from the electrical network cannot be resolved for any reasons, the built-in 50- and 60-Hz filter in PowerLab can sometimes improve results
The pressure and/or volume signal is noisy and shows irregular pattern	If all of the above fail and the noise is irregular, check if it disappears with another catheter. If so, the first catheter is most likely damaged. Check catheter for damage under the microscope, and if the coating is disrupted, clean and send it immediately to the manufacturer for further evaluation and repair. Always have at least one or two backup catheters before starting a study
The pressure sensor shows an excessive amount of drift, and/or it is not possible to ‘zero balance’ the pressure transducer output	Fluid may have gotten inside the catheter, or the pressure sensor diaphragm may be cracked or broken. It is possible to check the functionality of the pressure sensor by connecting an ohmmeter (resistance gauge) across the pins of the pressure sensor connector. The bridge on the Millar sensor should have symmetrical input and output impedances of approximately 1,000 ohms. If either reading is dramatically different from 1,000 ohms, there are chances that the pressure sensor is broken because of the above-mentioned reasons. Please contact Millar Instruments' customer support
The pressure sensor appears to be functional, but the readings are off by approximately 25 or 100 mm Hg	The pressure calibration in the data acquisition hardware is incorrect. Recalibrate the pressure signal in the data acquisition software according to the manufacturer's instructions. Briefly, the pressure control side of the MPVS-300/400 has three calibration settings. The settings are 0, 25 and 100 mm Hg. The standardized pressure output from the MPVS-300/400 is 1 V per 100 mm Hg. Therefore, the 0 mm Hg calibration setting corresponds to 0 V output, 25 mm Hg corresponds to 250 mV (0.25 V) output, and 100 mm Hg corresponds to 1 V output. In the case where the pressure readings are off by exactly 25 or 100 mm Hg, the wrong units label has been assigned to the voltage output coming out of the MPVS-300/400 for a particular calibration setting (e.g., the 25 mm Hg units label was assigned to 0 V out rather than 0 mm Hg units label)
The zero balanced pressure sensor in saline or distilled water drifts a few mm Hg after insertion into the biological environment	The most likely reason is that the catheter was not properly prepared before inserting it to the animal. Presoak the catheter tip in saline at body temperature for at least 30 min before use (e.g., by inserting the tip (but not the connectors) through the tip of a 1-ml syringe containing physiological saline solution)
The volume/conductance signal output from the MPVS-300/400 appears to drift	Electronic hardware has some drift present in the signal as a result of the electronic components heating up. To minimize conductance signal drift from the MPVS-300/400, turn it on and let it warm up at least 30 min before calibrating the output and using the catheter to collect PV data
The calibrated volume signal is larger than expected	Following the cuvette calibration, the volume signal (converted from RVUs to uLs) is larger than expected. The reason for this is that the parallel volume contribution of the myocardium (parallel conductance, which refers to the conductivity of the heart muscle that surrounds the left ventricular blood pool) has not been taken into account. Perform hypertonic saline calibration to correct for Vp
The conductance/volume signal is out of range	In larger animals with dilated cardiomyopathy, the conductance signal may go out of the range. Measure the ventricular length of the animal in question and make sure that the catheter being used has electrode spacing that matches this length (e.g., a 6-mm signal electrode spacing is appropriate for small-sized rats and a 9-mm signal electrode spacing is appropriate for larger rats). In some cases, custom catheter design may be required; contact the manufacturer with such request
The volume/conductance outputs from the cuvette calibration are not consistent	Make sure that the cuvette with fresh heparinized blood (to avoid clotting) is at body temperature. Always properly clean the cuvette between uses. Center the catheter tip within the cuvette and submerge it (all four electrodes should be submerged) in the blood, and hold it as steady as possible for 10–20 s in each well (normally using the first 1–5 wells is sufficient)