Exercise training decreases intercostal and transversus abdominis muscle blood flows in heart failure rats during submaximal exercise
Introduction
A hallmark characteristic of the heart failure (HF) syndrome is impaired exercise capacity. The underlying pathophysiological mechanisms responsible for this exercise limitation are multifactorial but include impaired cardiac output and exaggerated sympathetically-mediated vasoconstriction, consequently impairing locomotor muscle blood flow (BF) (Poole et al., 2012). HF patients also exhibit pulmonary system abnormalities at rest and during exercise (e.g., obstructive-resistive lung disorders, increased physiologic dead space, and ventilation/perfusion mismatch) (Olson et al., 2006; Poole et al., 2012; Smith and Olson, 2019). Further, HF patients exhibit an exaggerated ventilatory response, work of breathing, and subsequent respiratory muscle (i.e. diaphragm) BF response during submaximal exercise (Cross et al., 2012; Musch, 1993; Smith et al., 2018, 2017a; Smith and Olson, 2019). The reduced cardiac output reserve coupled with the elevated diaphragm BF in HF has important implications regarding cardiac output distribution during exercise (Borghi-Silva et al., 2008; Olson et al., 2010; Smith et al., 2020). Specifically, experimentally unloading the respiratory muscles in HF patients during submaximal exercise elicits decreases in leg vascular resistance and increases in leg BF, culminating in improvements in exercise tolerance (Borghi-Silva et al., 2008; Olson et al., 2010; Smith et al., 2020). Thus, therapeutic interventions aimed at unloading the respiratory muscles have the potential to mitigate the potential cardiac output redistribution from the locomotor to the respiratory muscles during submaximal exercise.
Exercise training is a clinically relevant treatment strategy (e.g., cardiac rehabilitation) that elicits beneficial pulmonary system adaptations in patients with HF (Hirai et al., 2015). Specifically, exercise training in HF with reduced ejection fraction (HFrEF) improves lung diffusing capacity, pulmonary gas exchange efficiency, and respiratory muscle strength (Adamopoulos et al., 2014; Guazzi et al., 2004; Winkelmann et al., 2009). Further, the ventilatory response during submaximal exercise at the same absolute workload is attenuated following exercise training in HF (Coats et al., 1992; Sullivan et al., 1989). It is unclear, however, if these exercise training-induced adaptations (particularly the attenuated ventilatory response) reduce the respiratory muscle metabolic requirement and subsequent BF response during submaximal exercise in HF. Therefore, the purpose of the present study was to determine the impact of exercise training on respiratory muscle (diaphragm, intercostal, and transversus abdominis) BFs and vascular conductances (VC) in HF rats during submaximal exercise at the same absolute workload. We hypothesized that diaphragm BF and VC would be lower in exercise-trained HF rats relative to their sedentary counterparts.
Section snippets
Ethical approval
The present study focuses on the impact of exercise training on respiratory muscle BF in HF rats in which a subset of these HF rats was used in a previously published investigation (Hirai et al., 2018). In the previously published investigation, young adult male Sprague-Dawley rats received a myocardial infarction (MI) under aseptic conditions as previously discussed (Hirai et al., 2018; Musch and Terrell, 1992), resulting in rats with moderate HF as indicated by heart morphometrics. The
Body weight and heart morphometrics
Body and diaphragm weights, heart morphometrics, and V̇O2max for HF + Sed and HF + ExT are shown in Table 1. Body weight and V̇O2max were higher for HF + ExT compared to HF + Sed (all, p < 0.05). Infarct size was greater for HF + Sed than HF + ExT (p < 0.05). No differences were present in diaphragm or lung weight ratios to body weight, LVEDP, or LV dP/dt between the HF + Sed and HF + ExT groups (all, p > 0.05). The lung weight ratio to body weight, LVEDP, and LV dP/dt in both groups are
Major findings
The present investigation is the first to determine the effect of exercise training on respiratory muscle BFs in HF rats during submaximal exercise. In contrast to our hypothesis, diaphragm BFs and VCs were not different between the HF + Sed and HF + ExT groups during exercise. However, we found that the HF + ExT had lower intercostal and transversus abdominis BFs and VCs than HF + Sed during submaximal exercise. These results indicate that exercise training can attenuate intercostal and
Funding
This work was supported by the National Institutes of Health (HL-2-108328 to DCP, T32 HL07111 to JRS, and K12 HD065987 to JRS), American Heart Association (Grant-in-Aid 10 GRANT 4350011 to DCP), Kansas State University College of Human Ecology (Postdoctoral Fellowship to DMH), and Purdue University (EVPRP PRF Faculty Grant to DMH). This work was also supported by grants from the National Institutes of Health, National Institute of General Medical Sciences, IDeA Networks of Biomedical Research
Declaration of Competing Interest
The authors report no declarations of interest.
References (33)
- et al.
Type II diabetes accentuates diaphragm blood flow increases during submaximal exercise in the rat
Respir. Physiol. Neurobiol.
(2020) - et al.
Neuronal nitric oxide synthase regulation of skeletal muscle functional hyperemia: exercise training and moderate compensated heart failure
Nitric Oxide
(2018) - et al.
Respiratory muscle training improves chemoreflex response, heart rate variability, and respiratory mechanics in rats with heart failure
Can. J. Cardiol.
(2017) - et al.
The effect of exercise training with an additional inspiratory load on inspiratory muscle fatigue and time-trial performance
Respir. Physiol. Neurobiol.
(2016) - et al.
Effect of chronic heart failure in older rats on respiratory muscle and hindlimb blood flow during submaximal exercise
Respir. Physiol. Neurobiol.
(2017) - et al.
Dietary nitrate supplementation opposes the elevated diaphragm blood flow in chronic heart failure during submaximal exercise
Respir. Physiol. Neurobiol.
(2018) - et al.
Intercostal muscle blood flow is elevated in old rats during submaximal exercise
Respir. Physiol. Neurobiol.
(2019) - et al.
Combined aerobic/inspiratory muscle training vs. aerobic training in patients with chronic heart failure: The Vent-HeFT trial: a European prospective multicentre randomized trial
Eur. J. Heart Fail.
(2014) - et al.
Effects of respiratory muscle unloading on leg muscle oxygenation and blood volume during high-intensity exercise in chronic heart failure
Am. J. Physiol. Heart Circ. Physiol.
(2008) - et al.
Controlled trial of physical training in chronic heart failure. Exercise performance, hemodynamics, ventilation, and autonomic function
Circulation
(1992)