INTRODUCTION: Negative pressure breathing is breathing with decreased pressure in the respiratory tract without lowering pressure acting on the torso. We lowered air pressure only during inspiration (NPBin). NPBin, used to increase venous return to the heart, is considered a countermeasure against redistribution of body fluids toward the head during spaceflight. We studied NPBin effects on circulation in healthy humans with an emphasis on NPBin-induced oscillations of hemodynamic parameters synchronous with breathing. We propose an approach to analyze the oscillations based on coherent averaging. METHODS: Eight men ages 24–42 yr participated in the NPBin and control series. During the series, to reproduce fluids shift observed under microgravity, subjects were supine and head down (−8°). Duration of NPBin was 20 min, rarefaction −20 cm H2O. Hemodynamic parameters were measured by Finometer. Electrical impedance measurements were used to estimate changes in blood filling of cerebral vessels. RESULTS: Mean values of hemodynamic parameters virtually did not change under NPBin, but NPBin induced oscillations of the parameters synchronous with respiration. Peak-to-peak amplitude under NPBin were: mean arterial pressure, 4 ± 1 (mmHg); stroke volume, 7 ± 3 (mL); and heart rate, 4 ± 1 (bpm). Electrical impedance of the head increased during inspiration. The increase under NPBin was three times greater than under normal breathing. DISCUSSION: Analysis of oscillations gives more information than analysis of mean values. NPBin induces short-term decrease in left ventricle stroke volume and arterial blood pressure during each inspiration; the decrease is compensated by increase after inspiration. NPBin facilitates redistribution of body fluids away from the head. Semenov YS, Melnikov IS, Luzhnov PV, Dyachenko AI. Oscillations of hemodynamic parameters induced by negative pressure breathing in healthy humans. Aerosp Med Hum Perform. 2024; 95(6):297–304.
An example of heart rate (HR) and mouth pressure (Pm) recordings illustrating the method for data analysis. A) A fragment of the original recording; B) overlaid frames that correspond to individual breathing cycles obtained from the fragment shown in panel A (markers of points on panels A and B correspond to individual frames); and C) overlaid frames of complete recording, the vertical lines mark the edges of an average inspiration.
The mean respiratory oscillations of heart rate (HR) in the group of volunteers. The results are obtained A) before NPBin, B) under NPBin, and C) after NPBin in the control series (dashed) and NPBin series (solid). The vertical lines mark the edges of an inspiration. Thin lines indicate the ± SD interval and bold lines indicate the mean curve of the group. The prefix “d” indicates that calculation was performed for changes in the parameter from its mean value.
The mean respiratory oscillations of central hemodynamic and head electrical bioimpedance parameters in the group of volunteers at the NPBin stage. The control series is shown as a dashed line, the NPBin series is shown as a solid line. Vertical lines mark the edges of an inspiration. Thin lines indicate the ± SD interval and bold lines indicate the mean curve for the group of volunteers. The prefix “d” indicates that calculation was performed for changes in the parameter from its mean value. SAP: systolic arterial pressure; DAP: diastolic arterial pressure; MAP: mean arterial pressure; SV: stroke volume; CO: cardiac output; TPR: total peripheral resistance; slowR: variable component (0.07–0.5 Hz) of the impedance modulus signal, left and right side of the head, respectively.
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