Cardiorespiratory reference data in norwegian post-myocardial infarction patients
Authors: Svenningsen A 
Published: May 2022

Abstract

Funding Acknowledgements
Type of funding sources: Public Institution(s). Main funding source(s): Funding received from the Norwegian University of Science and Technology (NTNU) as a student in the Master of Science in Physical Activity and Health programme.

Background/Introduction
Individuals with cardiovascular disease are typically excluded in studies aiming to present normative values for cardiorespiratory fitness (CRF) (1-5). Thus, there does not exist reference values for key cardiorespiratory variables in myocardial infarction (MI) patients, which can serve an important purpose of predicting prognosis and in designing individualized rehabilitation and secondary prevention programs required to improve CRF (6).

Purpose
To establish objectively measured reference values for key cardiorespiratory variables in Norwegian non-institutionalized men and women (18-79 years), with a history of myocardial infarction (MI) within the time period 2013-2020.

Methods
In total, 70 (18 women) participants were randomly selected from the ongoing Norwegian Trial of Physical Exercise After Myocardial Infarction and underwent cardiopulmonary exercise testing, using an individualized graded protocol while walking or running on a treadmill. Sub-maximal and peak values for key cardiorespiratory variables were measured using the MetaLyzer II ergospirometry system for mixing chamber gas analysis. Data were transferred from MetaSoft Studio software to eForsk, the data management system used for electronic case report forms in this study. eForsk is a standalone form-based information and communications technology solution for electronic collection of data developed by the Central Norway Regional Health Authority’s IT department (Hemit).

Results
Mean age was 64.9±8.5 and 63.7±9.4 years, body mass index 28.2±3.6 and 27.6±5.4 and peak oxygen uptake (V ̇O2peak) (mL·kg·min−1) 31.61±7.97 and 25.66±6.1 for men and women, respectively. Men aged &lt;65 years had the highest peak minute ventilation (112.3±27.3 L.min-1) and -tidal volume (2.67±0.45 L), with 18% (p=0.004) and 17% (p&lt;0.001) lower values, respectively, in men aged &gt;65 years. Peak ventilation (65.1±16.2 L.min-1) and tidal volume (1.68±0.41 L) were lower compared to men, but similar in both age groups among women. Ventilatory anaerobic threshold (VThan) and respiratory compensation point were observed at approximately 73% and 90% of V ̇O2peak for both sexes. Men &gt;65 years had 5% (p&lt;0.001) higher VThan (%V ̇O2peak) than men &lt;65 years. No such difference was observed among women. The ventilatory equivalent for CO2 at VThan (EqV ̇CO2VThan) in men &lt;65 years (30.5±2.9) was significantly lower compared to peers &gt;65 years (34.3±3.7), indicating 11% (p&lt;0.001) better ventilatory efficiency in the youngest age group. EqV ̇CO2VThan in women (29.6±2.8 vs 29.4±3.4) was similar for those aged above/below 65 years.

Conclusion(s)
This is the first reference material of its kind, establishing normative values for- and associations between key cardiorespiratory variables in a specific Norwegian MI population.