Integration of Brain Tissue Saturation Monitoring in Cardiopulmonary Exercise Testing in Patients with Heart Failure

Summary

This protocol integrated near-infrared spectroscopy into conventional cardiopulmonary exercise testing to identify the involvement of the cerebral hemodynamic response in exercise intolerance in patients with heart failure.

Abstract

Cerebral hypo-oxygenation during rest or exercise negatively impacts the exercise capacity of patients with heart failure with reduced ejection fraction (HF). However, in clinical cardiopulmonary exercise testing (CPET), cerebral hemodynamics is not assessed. NIRS is used to measure cerebral tissue oxygen saturation (SctO₂) in the frontal lobe. This method is reliable and valid and has been utilized in several studies. SctO₂ is lower during both rest and peak exercise in patients with HF than in healthy controls (66.3 ± 13.3% and 63.4 ± 13.8% vs. 73.1 ± 2.8% and 72 ± 3.2%). SctO₂ at rest is significantly linearly correlated with peak VO₂ (r = 0.602), oxygen uptake efficiency slope (r = 0.501), and brain natriuretic peptide (r = -0.492), all of which are recognized prognostic and disease severity markers, indicating its potential prognostic value. SctO₂ is determined mainly by end-tidal CO₂ pressure, mean arterial pressure, and hemoglobin in the HF population. This article demonstrates a protocol that integrates SctO₂ using NIRS into incremental CPET on a calibrated bicycle ergometer.

Introduction

Cardiopulmonary exercise testing (CPET) has been applied in patients with heart failure with reduced ejection fraction (HF) for multiple aims, including the quantification of cardiopulmonary fitness, prognosis, diagnosing causes of exercise limitations, and exercise prescriptions^1,2,3. During testing, hemodynamic variables and data derived from automatic gas exchange are monitored and analyzed. Cerebral tissue oxygen saturation (SctO₂) monitoring has value for grading prognosis and disease severity^4,5.

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Protocol

The following protocol was approved by the ethics committee in Chang Gung Memorial Hospital, Linkou, Taiwan. The exercise test was carried out in an air-conditioned laboratory with an atmospheric temperature of 22-25 °C, pressure of 755 to 770 Torr, and relative humidity of 55-65%. Before each test, the gas analyzer was calibrated following the manufacturer's instructions using room air and a gas mixture of known concentration (FO₂: 0.12; FCO₂: 0.05; N₂ as balance). The turbine flow meter of the system was calibrated by the 2-point method with 0.2 L/s and 2 L/s by an automatically-pumping system.

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Results

Thirty-four HF patients and 17 healthy controls were enrolled at Linkou Chang Gung Memorial Hospital, Taiwan. Each subject underwent cardiopulmonary exercise testing that incorporated SctO₂ monitoring by NIRS. Briefly, SctO₂ (rest; peak) values were significantly lower in the HF group (66.3 ± 13.3%; 63.4 ± 13.8%,) than in the control (73.1 ± 2.8%; 72 ± 3.2%) group (Figure 1). In the HF group, SctO₂ at rest (SctO_2rest

Discussion

Cerebral oxygenation monitored noninvasively and continuously by NIRS has been applied in various scenarios, including cardiovascular surgery¹³ and brain functional analyses such as those that estimate neural activity¹⁴. This protocol integrated NIRS into conventional CPET to identify the involvement of the cerebral hemodynamic response in exercise intolerance in patients with HF. It increases the value of exercise testing in determining prognosis and disease severity.

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Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bicycle ergometer	Ergoline, Germany	Ergoselect 150P
Cardiopulmonary exercise testing gas analysis	Cardinal-health Germany	MasterScreen CPX
Finger pulse oximetry	Nonin Onyx, Plymouth, Minnesota	Model 9500
Sphygmomanometer	SunTech Medical, UK	Tango
Near-infrared spectroscopy	CAS Medical Systems, Inc., Branford, CT	FORE-SIGHT system