Test of incremental respiratory endurance as home-based, stand-alone therapy in chronic obstructive pulmonary disease: A case report

Abstract

BACKGROUND

The prevalence of chronic obstructive pulmonary disease (COPD) is increasing worldwide, and at the same time it is associated with increased mortality and reduced quality of life. Efforts to build sustainable rehabilitation approaches to COPD treatment and prevention are crucial. The system of long-term pulmonary rehabilitation care is insufficient. The main reasons for the absence of these outpatient programs are the lack of experience, the lack of interest of insurance companies in secondary prevention programs, and the lack of healthcare facilities in large geographical areas. The possibility of at-home pulmonary rehabilitation models (telemonitoring and telecoaching) could solve this problem.

CASE SUMMARY

A 71-year-old man with severe COPD, Global Initiative for Obstructive Lung Diseases stage 3 underwent an 8-wk remotely monitored inspiratory muscle training with a device based on the test of incremental respiratory endurance method. Spirometry, body plethysmography, test of incremental respiratory endurance examination, 6-min walking test, body mass index, airflow obstruction, dyspnea, exercise capacity index, and subjective perception of dyspnea were performed as part of the initial and final examination. The patient performed training at home, and the physiotherapist monitored the patient remotely through a web application that allowed the physiotherapist to evaluate all training parameters in real-time and respond to any problems. After 8 wk of home training, there was a significant increase in all monitored values: maximal inspiratory pressure, a novel parameter sustained maximal inspiratory pressure, forced expiratory volume in 1 s, total lung capacity, forced vital capacity, peak expiratory flow, and inspiratory capacity. There was also an improvement in the perception of dyspnea according to the COPD Assessment Test and a modified Medical Research Council Breathlessness Scale, an increase in exercise tolerance according to the 6-min walking test, and a decrease in the exercise capacity index as a predictor of prognosis.

CONCLUSION

Respiratory telerehabilitation was greatly beneficial in a cooperative patient with COPD and may represent an alternative therapeutic approach to the increasing incidence of all lung diseases.

Key Words: Chronic obstructive pulmonary disease, Test of incremental respiratory endurance, Inspiratory muscle training, Telerehabilitation, Case report

Core Tip: Inspiratory muscle training with a telerehabilitation device motivated a patient to participate actively and be more responsible for his health. The test of incremental respiratory endurance allows remote monitoring of the patient’s inspiratory muscle training in real-time, while the training goal is automatically adjusted based on a patient’s inspiratory performance and status before the start of each inspiratory muscle training session. Also, the novel sustained maximal inspiratory pressure may be a more sensitive predictor of chronic obstructive pulmonary disease severity than the current commonly used maximal inspiratory pressure.

INTRODUCTION

The prevalence of chronic obstructive pulmonary disease (COPD) has increased worldwide and is associated with increased mortality and reduced quality of life[1]. In the Czech Republic, the estimated prevalence is about 800000 patients (7%-8%) affected by COPD[2]. Therefore, pulmonary rehabilitation should be an integral part of the comprehensive treatment of patients with COPD. However, there is still no effective system of lifelong pulmonary rehabilitation in the Czech Republic or abroad. Thus, there is a large discrepancy between the theoretical need and these programs actual existence and availability[1,3]. The solution to this problem could be the possibility of domestic models of pulmonary rehabilitation. In 2015, the American Thoracic Society and the European Respiratory Society published a political statement committing themselves to promote and expand home pulmonary rehabilitation that is evidence-based and accessible to most COPD patients[4]. Based on the results of meta-analyses, it is proven that technologies developed for telerehabilitation are essential because they improve mouth pressures, lung function, and quality of life[5,6]. New technologies have expanded potential opportunities for pulmonary rehabilitation, increasing the efficiency of home training and removing barriers through telemonitoring, telecoaching, and virtual reality[7,8]. This clinical case aims to report on a patient with COPD who performed inspiratory muscle training (IMT) with the PrO2® device (Design Net, Smithfield, United States), which enabled remote monitoring and evaluation of IMT in real-time using a cloud-based online platform. This case report demonstrates the substantial benefits of respiratory telerehabilitation in an epidemiologically serious disease such as COPD.

Additionally, patients see the real-time achievement of their goals during PrO2 IMT, which had a very motivating effect and likely improved his adherence to respiratory telerehabilitation. The PrO2 automatically adjusts the IMT program based on a patient’s inspiratory performance and status before the start of each IMT session, decreasing the need to physically visit the patient or the patient to visit the physiotherapist. Furthermore, IMT parameters (i.e. workload, number of breaths) can be adjusted remotely via the PrO2 app, making such IMT extremely useful clinically. We report on the substantial benefits of an innovative IMT program using the test of incremental respiratory endurance (TIRE) with the PrO2 device via telemonitoring.

CASE PRESENTATION

Chief complaints

A 71-year-old man with severe COPD with rapidly progressing dyspnea, low exercise tolerance, and hypoxemia.

History of present illness

The patient was diagnosed with COPD in 2010. Over the last 5 years, the patient experienced a gradual progression of dyspnea that limited his performance of everyday activities.

History of past illness

In 2019, the patient underwent Bentall’s heart surgery with resection of the left atrial appendage. The patient did not claim any diseases of affluence.

Personal and family history

The patient has a 30 pack-year history (20 cigarettes a day for 30 years) and has not smoked since 2008. He works as a managing director and denies any risk factors for lung disease from his occupation. His father contracted tuberculosis after the Second World War and died of lung cancer, and his brother has diabetes mellitus.

Physical examination

The patient was afebrile with alveolar respiration and sinus rhythm, and his lower limbs were without swelling.

Laboratory examinations

Alpha1-antitrypsin levels were normal. Arterial blood gas examination showed an oxygen partial pressure pO₂ = 7.67 kPa; carbon dioxide partial pressure pCO₂ = 4.56 kPa; pH = 7.46; and blood saturation SpO₂ = 90%.

Imaging examinations

Computed tomography results demonstrated centrilobular emphysema bilaterally reflecting a severe obstructive ventilation disorder.

Further diagnostic work-up

The patient underwent spirometry and body plethysmography examinations with the following results: forced expiratory volume in 1 s = 1.07 L; forced vital capacity = 1.94 L; inspiratory capacity = 1.57 L; total lung capacity (TLC) = 5.51 L; peak expiratory flow = 3.38 L. Inspiratory muscle performance was examined with the PrO2 device (Design Net, Smithfield, United States), showing the following results: maximal inspiratory pressure (MIP) = 57 cmH₂O; sustained maximal inspiratory pressure (SMIP) = 404 PTU (pressure-time unit); inspiratory duration (ID) = 7.7s; and fatigue index test (FIT) = 12.1. Questionnaires assessed the subjective perception of dyspnea with a COPD Assessment Test score of 15 and modified Medical Research Council Breathlessness score of 3. The six-minute walk test (6-MWT) was used to assess exercise tolerance, with the distance walked being 270 m, and the oxygen saturation decreased from 95% at baseline to 75% during the test. The multifactorial body mass index, airflow obstruction, dyspnea, and exercise (BODE) index was used as a predictor of prognosis with an initial score of 5. The Charlson Comorbidity Index calculated the 10-year mortality risk to be 53%.

FINAL DIAGNOSIS

Severe COPD [Global Initiative for Obstructive Lung Diseases (GOLD) stage 3] with rapid progression of exercise intolerance.

TREATMENT

The patient underwent an 8-wk, remotely monitored IMT program with a PrO2 device (Design Net, Smithfield, United States) at the University Hospital Brno between May and June 2021. The PrO2 device is protected by the United States Patent Application Publication No.: US 2017/0020439 A1. The Ethics Committee approved the project of the University Hospital Brno (01-020420/EK), and the patient also signed informed consent. After the previously described initial examinations, the patient was educated on using the PrO2 device, which was provided to use at home during the study period. Furthermore, the patient was educated about the IMT schedule and how to operate the device, and he received a training diary in which he regularly recorded notes of individual IMT sessions, including the rating of subjective workload using the Rating of Perceived Exertion as well as any subjective difficulties or technical problems.

Training description

The PrO2 device must first be connected via bluetooth to a tablet that the patient also received as part of the study. The PrO2 app must be downloaded to the tablet, which then serves as a monitor for the PrO2 device so that IMT can be viewed by the patient and remotely. The app automatically prompts the user to perform a maximal inspiratory maneuver from residual volume to total lung capacity, which was always performed three times with the greatest inspiratory effort used for IMT by providing a template at a specific percentage of the MIP and SMIP that the patient used for visual biofeedback during all IMT sessions. The PrO2 app was used to set the patient’s workload at 50% of the MIP and SMIP from the greatest inspiratory maneuver obtained before each IMT session, which was repeated for each IMT session of the study period, thus providing a new and up-to-date MIP and SMIP IMT template for each IMT session. The workload, therefore, was automatically adapted to the patient’s actual condition and level of inspiratory muscle performance, thereby ensuring a safe and high rate of IMT progress, which is not possible with other IMT devices. The patient’s goal during all IMT sessions was to inspire throughout at least 90% of the IMT area under the curve template, which if successful allowed the patient to progress to the next breath. However, if less than 90% of the IMT area under the curve template is achieved during IMT, the patient is prompted to inspire again with greater force to achieve 90% of the template. If the patient was unable to achieve 90% of the IMT template after three attempts, the IMT session was terminated to prevent excess fatigue and terminate ineffective IMT. The graphically and numerically evaluated MIP and SMIP template provides motivational biofeedback for the individual to continue improving his/her inspiratory efforts. The total number of breaths achieved during an IMT session and the MIP and SMIP template achieved with each inspiration were summed, providing an accumulated SMIP, which provided another key measurement of endurance from TIRE PrO2 IMT and associated app. A complete TIRE workout workload consists of 36 breaths, and the sum of the total area under the curve of all 36 breaths is provided, yielding endurance and inspiratory work achieved during each IMT session. After each IMT session, all IMT results described above were automatically transferred from a mobile phone or tablet housing the app to the appropriate account created on the website: www.pro2fit.com. These results were remotely and individually assessed by a physiotherapist who provided feedback (telemonitoring) to the patient, including patient motivation as well as reasons for not achieving the current daily goal (telecoaching), among other IMT issues.

The standard TIRE IMT session consists of six levels (A-F), with each level consisting of 6 breaths yielding 36 breaths. There is a fixed rest period between breaths at each level, which gradually decreases from 60 s (level A) to 10 s (level F). This is a clinically proven training protocol preset in the PrO2 device but can be changed via the app. The training frequency for the case subject was 4 times a week for 8 wk[9].

OUTCOME AND FOLLOW-UP

After 8 wk of IMT with the PrO2 device (adherence to IMT was 93%) (Table 1), the same examinations and tests performed at baseline were performed again, with the following results: forced expiratory volume in 1 s = 1.18; forced vital capacity = 2.12 L; inspiratory capacity = 1.95 L; TLC = 6.47 L; peak expiratory flow = 3.88 L; pO₂ = 6.81 kPa; pCO₂ = 5.39 kPa; pH = 7.42; SpO₂ = 89%; MIP = 107 cmH₂O; SMIP = 524P TU; ID = 15 s; FIT = 21.8; COPD Assessment Test = 4, Medical Research Council Breathlessness = 2. During 6-MWT, the patient’s performance improved to 330 m, and the decrease in oxygen saturation was substantially smaller (from 94% to 88%). The BODE index decreased to 4 (Table 2).

Table 1 Training program and results.

Training date	Total power, PTU	Max MIP, cmH2O	Max FIT	Max power, PTU	Max time, s
01.07.2021 15:30	12.42	97	15	385	15
29.06.2021 16:03	13.52	109	17	393	17
27.06.2021 15:31	10.78	86	16	337	19
25.06.2021 11:02	11.51	80	17	355	17
23.06.2021 15:59	12.65	82	19	392	17
21.06.2021 18:07	12.92	93	18	399	17
19.06.2021 12:51	16.84	77	20	396	19
17.06.2021 16:30	13.73	85	21	455	18
15.06.2021 18:12	11.95	80	22	426	18
13.06.2021 17:18	11.14	72	15	362	15
11.06.2021 14:55	13.12	77	22	412	19
09.06.2021 14:37	13.30	72	21	434	15
07.06.2021 16:36	12.75	76	23	426	16
05.06.2021 12:37	12.34	82	20	412	16
03.06.2021	No training - health indisposition
01.06.2021 15:38	12.97	75	20	441	16
30.05.2021 13:31	12.18	70	21	424	15
28.05.2021 14:57	11.40	76	17	390	14
27.05.2021 17:19	9.46	65	19	429	14
25.05.2021 15:35	12.98	61	26	439	20
23.05.2021 13:48	11.22	60	19	425	16
21.05.2021	No training - health indisposition
19.05.2021 17:21	10.29	54	15	328	14
17.05.2021 12:41	12.73	65	20	416	15
15.05.2021 15:31	14.32	53	14	339	11
13.05.2021 15:12	12.69	53	26	421	17
11.05.2021 11:13	13.53	55	32	457	17
09.05.2021 13:38	12.69	75	27	454	16
07.05.2021 11:37	11.40	78	15	434	15

PTU: Pressure time unit; MIP: Maximal inspiratory pressure; FIT: Fatigue index test.

Table 2 Changes of parameters before and after the test of incremental respiratory endurance.

Parameters	Before TIRE	After TIRE
MIP, cmH2O	57	107
SMIP-POWER, PTU	404	524
FIT	12.1	21.8
ID, s	7.7	15.0
FEV1, L	1.07	1.18
FVC, L	1.94	2.12
IC, L	1.57	1.95
TLC, L	5.51	6.47
PEF, L	3.38	3.88
mMRC	3	2

TIRE: Test of incremental respiratory endurance; MIP: Maximal inspiratory pressure; SMIP: Sustained maximal inspiratory pressure; PTU: Pressure time unit; FIT: Fatigue index test; ID: Inspiratory duration; FEV1: Forced expiratory volume in 1 second; FVC: Forced vital capacity; IC: Inspiratory capacity; TLC: Total lung capacity; PEF: Peak expiratory flow; mMRC: Modified Medical Research Council Breathlessness.

DISCUSSION

Patients with COPD suffer from reduced exercise tolerance and weakness of the inspiratory muscles, which is objectively represented by a significant reduction in the MIP, representing the maximum pressure obtained during inspiration from residual volume. The clinical and diagnostic significance of MIP is undisputable. However, it provides a rather limited view of inspiratory muscle performance and does not reflect the generation of pressure from residual volume to TLC[9]. Measurement of MIP, SMIP, and ID from the TIRE and PrO2 device has excellent rest-retest reliability and proven validity in known groups with COPD[10]. The advantage of TIRE examination and IMT is the evaluation and training of strength, endurance, power, and work aimed at the inspiratory muscles and providing several key parameters, including MIP, SMIP, ID, and FIT[10]. Thus, TIRE IMT may become a more effective way of IMT than currently established methods to employ IMT because of the muscular strength component reflected by MIP, the muscular endurance component represented by ID, and the power/work component reflected by the SMIP and the need to achieve at least 90% of SMIP area under the curve to progress to the next breath[9]. It is important to note that ID is not the standard length of inspiration but rather the inspiratory flow during maximal inspiratory efforts through a 2 mm orifice in the mouthpiece of the PrO2 device with isokinetic-like resistance from residual volume to TLC[10].

One key factor of TIRE PrO2 testing and training includes the SMIP, which represents single-breath inspiratory endurance and work capacity and is presented as the area under the pressure/time curve with the unit of measure being pressure time unit (PTU) and joule (J). The slope of the SMIP curve is also essential since too steep of slope represents a rapid decrease in inspiratory muscle strength, short ID, and poor SMIP. Thus, TIRE PrO2 evaluation and training provide a comprehensive assessment of inspiratory muscle performance and changes from IMT, which are provided graphically and numerically in the tablet app during all inspiratory efforts, enabling the patient to generate more excellent results of inspiratory maneuvers and pressures to achieve greater IMT efforts[9,10].

Our patient’s spirometry and body plethysmography values (forced expiratory volume in 1 s, forced vital capacity, inspiratory capacity, peak expiratory flow, TLC) also objectively improved, which is supported by other studies of IMT using other types of inspiratory training aids[11]. The increase in our case subject’s MIP, SMIP, and ID is significant since McCreery et al[12] showed a significant correlation between pulmonary function and inspiratory muscle performance examined via the TIRE MIP, SMIP, and ID. It is also worth noting the substantial improvement in our patient’s ID (almost 2 x more significant). A greater ID with more excellent airflow correlates with greater inspiratory muscle strength and the ability of the inspiratory muscles to generate more significant pressure for a longer period[9], which was associated with the substantial increase in MIP and SMIP in our case. The potential for further improvement of SMIP in our patient with COPD GOLD stage 3 will be limited after reaching a certain value because there appears to be a direct correlation between SMIP and the GOLD classification, and the SMIP of our patient is within the observed range for each GOLD classification group[9,10]. The increase in all TIRE parameters and thus an improvement in inspiratory muscle performance appears to have had a positive effect on the increase in the 6-MWT distance ambulated. A greater 6-MWT distance is associated with a better prognosis regarding fewer hospital readmissions and lower mortality risk in patients with COPD[13].

The substantial increase in FIT in our case subject was likely due to the intensive IMT program, which elicited greater inspiratory muscle strength, endurance, power, and work. According to Wüthrich et al[14], a higher FIT score appears to be associated with less propensity to inspiratory muscle fatigue.

It is important to note that SMIP correlates positively with the BODE index, and an improvement in SMIP through IMT may potentially yield longer survival in patients with COPD[15,16]. Our results reflect this possibility, with the BODE index decreasing from 5 to 4 after only 8 wk of IMT.

Surprisingly, despite all of the above improvements, the patient’s final arterial blood gas examination revealed a modest decrease in pO2 and a slight increase in pCO2. However, the patient did not report any adverse symptoms during the final testing, and the Tension Time Index parameter, which detects the risk of respiratory failure, was standard. In contrast, after 8 wk of IMT, there was a significant improvement in the subjective perception of dyspnea according to the Medical Research Council Breathlessness (3 to 2) and COPD Assessment Test (15 to 4) questionnaires. In view of these findings, further research is warranted examining the acute and long-term effects of IMT on pO₂, pCO₂, Tension Time Index, and the subjective perception of dyspnea. Furthermore, since the FIT measure from TIRE PrO2 testing is associated with propensity to fatigue, examination of the relationship between Tension Time Index and FIT would be extremely valuable due to the ease of obtaining FIT during several inspiratory maneuvers using the PrO2 device.

CONCLUSION

IMT via the TIRE and PrO2 device elicited substantial improvements in inspiratory muscle performance, which substantially improved pulmonary function, 6-MWT distance ambulated, COPD symptoms, and the BODE index. Further investigation of the new and quite novel SMIP parameter and the TIRE method of IMT appears warranted in patients with COPD and other diseases in which inspiratory muscle performance is impaired.