Effects of experimental hypovolemia and pain on pre-ejection period and pulse transit time in healthy volunteers

Abstract

Trauma patients may suffer significant blood loss, and noninvasive methods to diagnose hypovolemia in these patients are needed. Physiologic effects of hypovolemia, aiming to maintain blood pressure, are largely mediated by increased sympathetic nervous activity. Trauma patients may however experience pain, which also increases sympathetic nervous activity, potentially confounding measures of hypovolemia. Elucidating the common and separate effects of the two stimuli on diagnostic methods is therefore important. Lower body negative pressure (LBNP) and cold pressor test (CPT) are experimental models of central hypovolemia and pain, respectively. In the present analysis, we explored the effects of LBNP and CPT on pre-ejection period and pulse transit time, aiming to further elucidate the potential use of these variables in diagnosing hypovolemia in trauma patients. We exposed healthy volunteers to four experimental sequences with hypovolemia (LBNP 60 mmHg) or normovolemia (LBNP 0 mmHg) and pain (CPT) or no pain (sham) in a 2 × 2 fashion. We calculated pre-ejection period and pulse transit time from ECG and ascending aortic blood velocity (suprasternal Doppler) and continuous noninvasive arterial pressure waveform (volume-clamp method). Fourteen subjects were available for the current analyses. This experimental study found that pre-ejection period increased with hypovolemia and remained unaltered with pain. Pulse transit time was reduced by pain and increased with hypovolemia. Thus, the direction of change in pulse transit time has the potential to distinguish hypovolemia and pain.

Keywords: hypovolemia; non-invasive; pre-ejection period; pulse transit time.

FIGURE 1

Experimental sequences. The gray bar indicates the point where we have done our analyses, which represent the last 30 s of interventions. Lower body negative pressure (LBNP). Cold pressor test (CPT).

FIGURE 2

Pre‐ejection period (PEP) and pulse transit time (PTT).

FIGURE 3

Changes from baseline for the different sequences for (a) cardiac output, (b) stroke volume, (c) mean arterial pressure, and (d) heart rate. The bar indicates the point where we have done our analyses, which represent the last 30 s of interventions.

FIGURE 4

Changes from baseline for the different sequences for (a) pre‐ejection period (PEP), (b) pulse transit time (PTT), and (c) indexed pulse transit time (iPTT). The bar indicates the point where we have done our analyses, which represent the last 30 s of interventions.