Left ventricular twist is augmented in hypoxia by ß1-adrenergic-dependent and independent factors, without evidence of endocardial dysfunction
American Heart Association
MetadataShow full item record
Background. Left ventricular (LV) twist mechanics are augmented with both acute and chronic hypoxemia. Although the underlying mechanisms remain unknown, sympathetic activation and/or a direct effect of hypoxemia on the myocardium have been proposed, the latter of which may produce subendocardial dysfunction that is masked by larger subepicardial torque. This study therefore sought to i) determine the individual and combined influences of ß1-adrenergic receptor (ß1-AR) stimulation and peripheral O2 saturation (SpO2) on LV twist in acute and chronic hypoxia, and ii) elucidate whether endocardial versus epicardial mechanics respond differently to hypoxia. Methods. Twelve males (27±4yr) were tested near sea level (SL) in acute hypoxia (SpO2=83±3%) and following 3-6 days at 5050m (HA; SpO2=83±3%). In both settings, participants received infusions of ß1-AR blocker esmolol and volume-matched saline (double-blind, randomized). LV mechanics were assessed with 2-dimensional speckle-tracking echocardiography, and region-specific analysis to compare subendocardial and subepicardial mechanics. Results. At SL, compared to baseline (14.8±3.0º) LV twist was reduced with esmolol (11.2±3.3º; p=0.007) and augmented during hypoxia (19.6±4.9º; p<0.001), while esmolol+hypoxia augmented twist compared to esmolol alone (16.5±3.3º; p<0.001). At 5050m, LV twist was increased compared to SL (19.5±5.4°; p=0.004), and reduced with esmolol (13.0±3.8°; p<0.001) and SpO2 normalization (12.8±3.4°; p<0.001). Moreover, esmolol+normalized SpO2 lowered twist further than esmolol alone (10.5±3.1°; p=0.036). There was no mechanics-derived evidence of endocardial dysfunction with hypoxia at SL or HA. Conclusions. These findings suggest LV twist is augmented in hypoxia via ß1-AR-dependent and -independent mechanisms (e.g. 1-AR stimulation), but does not appear to reflect endocardial dysfunction.
Circulation: Cardiovascular Imaging;
Article published in Circulation: Cardiovascular Imaging available at https://doi.org/10.1161/CIRCIMAGING.118.008455
Funding was provided by the Natural Sciences and Engineering Research Council of Canada (P.N.A.), Canadian Research Chairs (P.N.A.) and The Physiological Society UK (A.M.W.).
- Sport Research Groups 
Showing items related by title, author, subject and abstract.
Impaired myocardial function does not explain reduced left ventricular filling and stroke volume at rest or during exercise at high altitude Stembridge, Mike; Ainslie, Philip; Hughes, Michael G.; Stöhr, Eric J.; Cotter, James D.; Tymko, Michael M.; Day, Trevor A.; Bakker, Akke; Shave, Rob (American Physiological Society, 2015-11-15)Impaired myocardial systolic contraction and diastolic relaxation have been suggested as possible mechanisms contributing to the decreased stroke volume (SV) observed at high altitude (HA). To determine whether intrinsic ...
Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans Vermeulen, T.; Boulet, L.; Stembridge, Mike; Williams, A.M.; Anholm, J.; Subedi, P.; Gasho, C.; Ainslie, Philip N.; Feigl, E.; Foster, G.E. (American Physiological Society, 2018-03-30)It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial PO2 and PCO2 or if coronary vascular responses are the result of concomitant increases in myocardial O2 consumption/demand ...
Intrinsic ventricular function does not explain reduced stroke volume at rest and during exercise at high altitude Stembridge, Mike; Ainslie, Philip; Stöhr, Eric J.; Tymko, Michael; Day, Trevor A.; Bakker, Akke; Hughes, Michael G.; Smith, K.J; Willie, C.K.; Lewis, N.C.S.; Shave, Rob (Japanese Society of Physical Fitness and Sports Medicine, 2015-01-25)Introduction: Both impaired systolic dysfunction and myocardial relaxation have previously been advanced as possible mechanisms contributing to decreased stroke volume (SV) at high altitude (HA). To determine whether ...