Reduction of left ventricular epicardial segment length by 100% oxygen breathing in open-chest dogs.

Abstract

We conducted this study in order to learn whether or not oxygen inhalation reduces left ventricular size, one of the major determinants of myocardial oxygen demand. In 11 open-chest dogs, a Mercury-in-Silastic gauge was applied to measure left ventricular circumferential length while the dogs were being ventilated with either room air or 100% oxygen. Four characteristic notches were identified on the resulting length curve : L1, length at the beginning of ejection; L2, length at the end of ejection; L3, length in early diastole; and L4, length at end diastole, L1 was shortened from 24.9+10.5 to 24.4+9.9 mm (a decrease of 1.4+2.1%) by oxygen breathing, L2 was also shortened from 26.8+11.5 to 26.2+10.7 mm (a decrease of 1.5+2.9%), L3 from 17.5+4.4 to 17.4±4.3 mm (a decrease of 0.7+ 2.7%) and L4 from 17.7±4.8 to 17.5±4.7 mm (a decrease of 1.3±2.4%). These changes all disappeared when the inspiratory gas was changed from oxygen back to air. Heart rate and left ventricular end-diastolic pressure showed no significant changes but were accompanied by a slight reduction in aortic pressure and myocardial contractile force. This study demonstrated a small but consistent reduction in left ventricular circumferential length by oxygen breathing. This reduction in left ventricular size will reduce left ventricular tension and thus result in reduction of left ventricular myocardial oxygen demand when oxygen inhalation is applied to patients with ischemic heart disease.--oxygen inhalation therapy; myocardium; myocardial ischemia; left ventricle

The beneficial effects of 40% and 100% O2 inhalations on acutely-induced myocardial ischemia in dogs.

“…Since left ventricular tension parallels left ventricular chamber size, a reduction in left ventricular size will cause a reduction in myocardial 02 consumption. Although left ventricular size was not measured in the present study, our previous studies with open-chest dogs (Ishikawa et al 1982) and in clinical patients (Ishikawa et al 1984) indicated consistent reductions of approximately 1 to 3% in left ventricular segment length. It is now evident that 02 inhalation causes a lower heart rate, a smaller contractile force and a smaller heart chamber size.…”