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Respiratory pump contributes to increased physiological reserve for compensation during simulated haemorrhage
Author(s) -
Poh Paula Y. S.,
Carter Robert,
HinojosaLaborde Carmen,
Mulligan Jane,
Grudic Gregory Z.,
Convertino Victor A.
Publication year - 2014
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2014.081208
Subject(s) - presyncope , decompensation , respiratory compensation , medicine , cardiology , anesthesia , respiratory system , blood pressure , placebo , vascular resistance , blood volume , hemodynamics , heart rate , physiology , anaerobic exercise , alternative medicine , pathology
New FindingsWhat is the central question of this study? The negative intrathoracic pressure created by inspiration (i.e. the respiratory pump) is associated with enhanced venous return, although its contribution as a potential mechanism of compensation during blood loss has not been quantified.What is the main finding and its importance? We demonstrated that optimizing the creation of negative intrathoracic pressure during inspiration represented a mechanism of compensation during haemorrhage that was quantifiably reflected in a reduced rate of diminution of the compensatory reserve, resulting in increased tolerance to progressive reductions in central blood volume.Intrathoracic pressure regulation (IPR) represents a therapy for increasing systemic circulation through the creation of negative intrathoracic pressure. We hypothesized that using this ‘respiratory pump’ effect would slow the diminution of the physiological reserve to compensate during progressive reductions in central blood volume. The compensatory reserve index (CRI) algorithm was used to measure the proportion (from 100 to 0%) of reserve capacity that remained to compensate for central volume loss before the onset of cardiovascular decompensation. Continuous analog recordings of arterial waveforms were extracted from data files of seven healthy volunteers. Subjects had previously participated in experiments designed to induce haemodynamic decompensation (presyncope) by progressive reduction in central blood volume using graded lower‐body negative pressure. The lower‐body negative pressure protocol was completed while breathing spontaneously through a standard medical face mask without (placebo) and with a resistance (approximately −7 cmH 2 O; active IPR) applied during inspiration. At the onset of presyncope in the placebo conditions, CRI was smaller than the CRI observed at the same time point in the active IPR conditions. The CRI at the onset of presyncope during active IPR (0.08 ± 0.01) was similar to the CRI at presyncope with placebo. Kaplan–Meier and log rank tests indicated that CRI survival curves were shifted to the right by active IPR. Optimizing the respiratory pump contributed a small but significant effect of increasing tolerance to progressive reductions in central blood volume by extending the compensatory reserve.