Oxygen uptake kinetics and chronotropic responses to exercise are impaired in survivors of severe COVID-19

Abstract

The post-acute phase of COVID-19 is often marked by several persistent symptoms and exertional intolerance, which compromise survivors' exercise capacity. This was a cross-sectional study aiming to investigate the impact of COVID-19 on oxygen uptake (VO2) kinetics and cardiopulmonary function in survivors of severe COVID-19 three to six months after intensive care unit (ICU) hospitalization. Thirty-five COVID-19 survivors previously admitted to ICU (5±1 months after hospital discharge) and 18 controls matched for sex, age, comorbidities, and physical activity level with no prior history of SARS-CoV-2 infection were recruited. Subjects were submitted to a maximal graded cardiopulmonary exercise test (CPX) with an initial 3-minute period of a constant, moderate-intensity walk (i.e., below ventilatory threshold, VT). VO2 kinetics was remarkably impaired in COVID-19 survivors as evidenced at the on-transient by an 85% (P=0.008) and 28% (P=0.001) greater oxygen deficit and mean response time (MRT), respectively. Furthermore, COVID-19 survivors showed a 11% longer (P=0.046) half-time of recovery of VO2 (T1/2VO2) at the off-transient. CPX also revealed cardiopulmonary impairments following COVID-19. VO2peak, percent-predicted VO2peak and VO2VT were reduced by 17%, 17% and 12% in COVID-19 survivors, respectively (all P<0.05). None of the ventilatory parameters differed between groups (all P>0.05). Additionally, COVID-19 survivors also presented with blunted chronotropic responses (i.e., chronotropic index, maximum heart rate, and heart rate recovery; all P<0.05). These findings suggest that COVID-19 negatively affects central (chronotropic) and peripheral (metabolic) factors that impair the rate at which VO2 is adjusted to changes in energy demands.

Post-COVID Syndrome and Cardiorespiratory Fitness—26-Month Experience of Single Center

“…Unfortunately, the study did not provide complete information about the medication of the patients. Similarly, in another study, the post-COVID patients had decreased chronotropic response, represented by decreased maximum heart rate, prolonged heart recovery time, and decreased chronotropic index [ 25 ]. In contrast with these results, we only found chronotropic incompetence in one patient.…”

“…Despite the extremely large numbers of studies dealing with COVID-19 and post-COVID syndrome, studies analyzing cardiorespiratory functions in post-COVID individuals are not as numerous. The vast majority of studies have confirmed that more severe COVID-19 infection leads to a more pronounced reduction in the exercise capacity [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Moreover, in all of the published studies, only a small number of patients were involved, and usually the involved individuals had survived more severe infection forms, or even individuals who were not discharged from the hospital.…”

Effects of a 16-week home-based exercise training programme on health-related quality of life, functional capacity, and persistent symptoms in survivors of severe/critical COVID-19: a randomised controlled trial

“…Exertional intolerance is a common feature following COVID-19, especially in severe forms of the disease 3 4. Potential mechanisms for reduced exercise capacity include altered central (cardiac, pulmonary and autonomic) and peripheral (metabolic) parameters.…”

“…System was calibrated immediately before each test following manufacturer’s specifications. Outcome variables, including peak oxygen uptake (VO 2peak ), oxygen uptake at ventilatory threshold (VO 2VT ), oxygen uptake efficiency slope (OUES), respiratory exchange ratio (RER), pulmonary ventilation (V E ), ventilatory equivalent for carbon dioxide (V E /V CO2 ), O 2 pulse and chronotropic index were assessed as previously described 3 15 16. Heart rate recovery was assessed during the first (HRR 1min ), second (HRR 2min ) and fourth minute (HRR 4min ) of the recovery phase.…”

“…It has been defined as newly occurring and persistent symptoms (eg, fatigue, dyspnoea, muscle weakness, etc) lasting more than 12 weeks that cannot be explained by an alternative diagnosis 2. This condition is usually associated with substantial health impairments, including poor cardiorespiratory fitness, exertional intolerance, reduced functional capacity, lower muscle mass and psychological morbidities (eg, anxiety and depression) 3–8. Available evidence suggests that patients who have had severe/critical COVID-19 (eg, those admitted to an intensive care unit) may present with even worse outcomes 9.…”