Nasal high-flow therapy reduces work of breathing compared with oxygen during sleep in COPD and smoking controls: a prospective observational study

Abstract

Patients with chronic obstructive pulmonary disease (COPD) endure excessive resistive and elastic loads leading to chronic respiratory failure. Oxygen supplementation corrects hypoxemia but is not expected to reduce mechanical loads. Nasal high-flow (NHF) therapy supports breathing by reducing dead space, but it is unclear how it affects mechanical loads of patients with COPD. The objective of this study was to compare the effects of low-flow oxygen and NHF therapy on ventilation and work of breathing (WOB) in patients with COPD and controls during sleep. Patients with COPD (n = 12) and controls (n = 6) were recruited and submitted to polysomnography to measure sleep parameters and ventilation in response to administration of oxygen and NHF. A subset of six patients also had an esophageal catheter inserted for the purpose of measuring WOB. Patients with COPD had similar minute ventilation (V̇e) but lower tidal volumes than matched controls. With oxygen, [Formula: see text]was increased and V̇e was reduced in both controls and patients with COPD, but there was an increase in transcutaneous CO₂ levels. NHF produced a greater reduction in V̇e and was associated with a reduction in CO₂ levels. Although NHF halved WOB, oxygen produced only a minor reduction in this parameter. We conclude that oxygen produced little change in WOB, which was associated with CO₂ elevations. On the other hand, NHF produced a large reduction in V̇e and WOB with a concomitant decrease in CO₂ levels. Our data indicate that NHF improves alveolar ventilation during sleep compared with oxygen and room air in patients with COPD and therefore can decrease their cost of breathing.

New & noteworthy: Nasal high-flow (NHF) therapy can support ventilation in patients with chronic obstructive pulmonary disease during sleep by decreasing the work of breathing and improving CO₂ levels. On the other hand, oxygen supplementation corrects hypoxemia, but it produces only a minimal reduction in work of breathing and is associated with increased CO₂ levels. Therefore, NHF can be a useful method to assist ventilation in patients with increased respiratory mechanical loads.

Keywords: COPD; nasal high flow; oxygen; sleep; work of breathing.

Fig. 1.

Study protocol during the intervention night (see text). Participants underwent polysomnography with EEG, EMG, $\mathrm{S}{\mathrm{a}}_{{\mathrm{O}}_2}$, and CO₂ monitoring. Additionally, individuals wore a mask attached to a pneumotacograph, allowing ventilation monitoring. Six patients also had an esophageal catheter inserted to measure work of breathing (WOB). During stable non–rapid eye movement (NREM) sleep, delivery through a nasal cannula was alternated among room air (no additional flow), oxygen (2 l/min), and nasal high flow (NHF) at 20 l/min. tcCO₂, transcutaneous CO₂, P_ES, esophageal pressure.

Fig. 2.

Ventilation and breathing parameters during stable NREM sleep under room air, oxygen or NHF conditions in subjects with chronic obstructive pulmonary disease (COPD, n = 12) and control subjects (n = 6). Both oxygen and NHF decreased minute ventilation (V̇e) and tidal volume, but the decrease was greater under the NHF condition. With oxygen, there was also a statistically significant but clinically irrelevant decrease in respiratory rate in the control group. Graphs represent averages ± SE. Repeated-measures ANOVA was used for comparing the three groups, with a Holm adjustment for two-group comparisons. *P < 0.05 for comparison with room air condition, #P < 0.05 for comparison with room air and oxygen conditions.

Fig. 3.

$\mathrm{S}{\mathrm{a}}_{{\mathrm{O}}_2}$ and transcutaneous CO₂ during stable NREM sleep under room air, oxygen, or NHF conditions in subjects with COPD (n = 12) and control subjects (n = 6). Oxygen significantly increased $\mathrm{S}{\mathrm{a}}_{{\mathrm{O}}_2}$, but it also led to a rise in CO₂ levels. Despite reducing V̇e (see Fig. 2), NHF decreased CO₂ levels and, in patients with COPD, slightly decreased $\mathrm{S}{\mathrm{a}}_{{\mathrm{O}}_2}$. Graphs represent averages ± SE. Repeated-measures ANOVA was used to compare the three groups, with a Holm adjustment for two-group comparisons. *P < 0.05 for comparison with room air condition, #P < 0.05 for comparison with room air and oxygen conditions.

Fig. 4.

WOB, pressure time product, and pressure swings during stable NREM sleep under room air, oxygen, or NHF conditions in a subset of six patients who had an esophageal catheter inserted. Although oxygen only minimally reduced WOB, NHF resulted in a large decrease in WOB. NHF also decreased esophageal pressure swings and pressure time product, but could not be noticed with the use of oxygen. Gray dashed lines represent individual values. Dark lines represent averages with SE bars. Repeated-measures ANOVA was used for comparing the three groups, with a Holm adjustment for two-group comparisons. Error bars depict high intragroup variability. The statistical test (repeated-measures ANOVA) corrects for this variability and evaluates changes on each individual under the different experimental conditions. *P < 0.05 for comparison with room air condition, #P < 0.05 for comparison with room air and oxygen condition.

Fig. 5.

Change in minute ventilation vs. change in WOB in the six subjects who agreed to the use of an esophageal catheter. Black symbols represent changes in WOB and V̇e with the use of NHF compared with room air. White symbols represent changes in WOB and V̇e with the use of oxygen compared with room air. The figure shows the close correlation between the two parameters, suggesting there are few changes in respiratory mechanics. The observed reduction in WOB parallels the reduction in V̇e. We can notice a greater change with the use of NHF compared with oxygen.