CORRELATIVE STUDIES OF THE PNEUMOCARDIOGRAM AS A NONINVASIVE INDICATOR OF CARDIAC STROKE VOLUME

JERRY L WESSALE, Purdue University

Abstract

Cardiac stroke volume (SV)--the volume of blood ejected by each cardiac ventricle per beat--is an important parameter for assessing overall cardiac performance. It has been suggested that the pneumocardiogram (PNCG)--a record of the pulsatile flow of air in the trachea coincident with each heart beat--may serve as a noninvasive indicator of SV. Studies were performed (1) to correlate (DELTA)V(,pncg), the volume of air that moves into the airway during ventricular ejection, with measured SV, (2) to develop techniques which permit calibrating (DELTA)V(,pncg) to yield true SV, and (3) to validate the use of these calibration techniques in the dog. In anesthetized, mongrel dogs the cardiogenic air flow through the endotracheal tube was measured with a pneumotachograph consisting of a capillary-tube (Fleisch no.2 ) air resistor and a specially designed, high-fidelity differential pressure transducer. The correlation between (DELTA)V(,pncg), obtained by integrating the PNCG over the period of ventricular ejection, and SV, measured by either the saline-dilution (SD) or the electromagnetic flowmeter (EM) methods, was determined for a wide range of SV. Although the PNCG tracked measured SV, (DELTA)V(,pncg) was always less. The range of linear regression coefficients (b(,1)) was 0.10 to 0.47; correlation coefficients (r) ranged from 0.55 to 0.98. In the calibration studies, intrathoracic volume was changed by injecting a known quantity of water into a lax intraesophageal bladder at a fixed flow rate and over a fixed duration. The concomitant volume of air that moved out of the lungs was a fraction of the intrathoracic (intraesophageal) volume change. Based on the results of the calibration studies, correction factors were developed for (1) the volume of venous blood returning to the thorax during ventricular ejection, and (2) the fraction of the thoracic volume change not coupled to the airway. SV determined from the "corrected" (DELTA)V(,pncg) was compared with SV measured by the SD and EM methods: b(,1) ranged from 0.61 to 1.48 (mean = 0.93); r ranged from 0.54 to 0.92 (mean = 0.72). The results suggest that the PNCG may be well suited for continuous tracking of changes in cardiac stroke volume on a noninvasive, beat-by-beat basis. The technique is ideally applicable to intubated human subjects, particularly those undergoing closed-chest surgical procedures.

Degree

Ph.D.

Subject Area

Anatomy & physiology|Animals

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