The Effects of Different Inspiratory Pressures on the Diaphragmatic Thickness Fraction and Sternocleidomastoid Muscle Activation in People After Stroke
Conditions: Stroke
Sponsor: Hong Kong Metropolitan University

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Research proposal 
 
1. Project title 
The effects of different inspiratory pressures on the diaphragmatic thickness fraction 
and sternocleidomastoid muscle activation in people after stroke   
 
2. Abstract 
This study is a cross-sectional study to determine the optimal inspiratory muscle 
training (IMT) intensity for stroke survivors. Participants will breathe through a 
pressure threshold inspiratory loading device with varying loads in random order. 
During the test, accessory inspiratory muscle (sternocleidomastoid muscles) activity 
will be measured with surface electromyography (sEMG) and diaphragm thickness will 
be used to assessed with ultrasonography. Repeated-measures ANOVA will be used for 
statistical analysis to determine the most effective training intensity.  
 
3. Project objectives 
Introduction: 
Stroke was the second largest cause of global death and disability in 2019 [1]. Direct 
medical costs for stroke in China was 50 billion yuan (nearly 7.69 billion US dollars) 
in 2015, and this accounted for the highest medical cost in China [2]. In 2016, the Global 
Burden of Disease (GBD) study estimated that the lifetime risk of stroke from the age 
of 25 years was 39.3% in China, which is the highest estimated risk in the world [3]. In 
2018, stroke was the third highest disease cause of death, accounting for 1.57 million 
deaths in China [4].  
 
Stroke not only causes impairment of motor function but can also affect lung function 
[5]. The lung function (e.g. forced vital capacity (FVC), forced expiratory volume in 
one second (FEV1), maximal inspiratory pressure (MIP), peak expiratory flow (PEF)) 
in people after stroke was reported significantly lower than the age and gender-matched 
healthy adults [6, 7]. Impaired lung function in people after stroke not only leads to 
high risk of pneumonia, poor functional outcomes and prolonged hospitalization but 
may also increase mortality [8-10].  
 
Diaphragmatic weakness is considered to be the major reason contributing to the 
reduction of lung function of people after stroke [11]. Diaphragm, as the primary 
inspiratory muscle, accounts for approximately 75% of the airflow into the lungs during 
quiet breathing [12]. However, most people after stroke have diaphragmatic weakness 
due to the loss of central motor control, leading to paralysis of the diaphragm in the 
contralateral side [13, 14]. Diaphragmatic weakness can lead to asymmetric respiratory 
chest movements, changes in the respiratory mechanism, and consequently reduced 
lung function [11, 14, 15]. The thickness of the affected diaphragm of patients after sub-
acute and chronic stroke was found only to have nearly 50% of those of healthy 
individuals [13]. Contraction of diaphragm fibers can be quantified by the diaphragmic 
thickening fraction (DTF), determined by “(thickness of the diaphragm at end 
inspiratory - thickness at end expiratory)/thickness at end expiratory” [16]. A reduction 
in diaphragmatic contraction was reported to be significantly correlated with decreased 
lung function (e.g. FVC, FEV1, MIP, PEF) in people after stroke [13, 17].  
 

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Inspiratory muscle training (IMT) is an intervention designed for improvement of 
inspiratory muscle (including the diaphragm) strength and endurance in healthy adults 
and patients suffering from different diseases (e.g. Parkinson, chronic obstructive 
pulmonary disease, cardiovascular disease) [18-21]. Regarding the IMT training 
protocol, the commonly reported training intensities varied between 30-80% of MIP in 
people after stroke [22-24]. Although the diaphragm is the primary inspiratory muscle, 
the use of IMT may not help improve the diaphragmatic contraction under some 
circumstances. Previous studies suggested that, in healthy adults and people receiving 
mechanical ventilation, when inspiratory load exceeds the capacity of the diaphragm 
(higher than 60% MIP), the accessory respiratory muscle (in particular the 
sternocleidomastoid muscle) would be activated dramatically, which would increase 
work of breathing and fatigue [25, 26]. Other studies also reported that high IMT 
intensity may have the risk to increase the work of breathing thereby leading to fatigue 
[27] or resulting in a decrease, rather than increase, in surface electromyography signals 
in diaphragmatic activity [27]. It is postulated that IMT recruits accessory muscles such 
as sternocleidomastoid rather than diaphragm during the practice [24]. Hence, 
evaluation of effectiveness of IMT on DTF in people after stroke and further 
investigation on determining an optimal training protocol including inspiratory effort 
and training intensity for recruiting diaphragmatic activities in the stroke population are 
warranted. 
 
 
Aims of the study: 
To determine the optimal training intensity that is associated with the strongest 
diaphragmic thickening fraction in people after stroke.  
 
 
Project significance:  
Outcomes of this project study will fill the existing knowledge gaps in the 
understanding of the relationship between inspiratory pressure and recruitment of 
diaphragmatic muscles in people after sub-acute and chronic stroke.  
 
4. Research methodology 
 
Study design: 
This study will be a cross-sectional study.  
 
Participants:  
Individuals who have had a stroke and healthy adults will be invited to participate in 
this study. 
 
Participants recruitment for people after stroke: 
The inclusion criteria are: (1) age ≥ 18 years; (2) clinically diagnosed with ischemic 
and/or hemorrhagic stroke; (3) duration of stroke range from 1 month to 12 months 
after diagnosis; (4) had no facial palsy, which could prevent proper labial occlusion; (5) 
had not undergone thoracic or abdominal surgery; (6) could understand and follow the 
verbal instruction; (7) stable cardiac conditions; (8) no previous history of respiratory 
problems. 
 

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The exclusion criteria are: (1) acute myocardial infarction or acute heart failure; (2) 
acute pain on chest or abdominal; (3) with the clinical signs of significant pulmonary 
disease; (4) consciousness impaired; (5) patient with nasal feeding tube, tracheal tube 
and/or any condition, which prevent the measurement or training. 
 
Recruitment of healthy participants: 
The inclusion criteria are: (1) age ≥ 18 years; (2) had not undergone thoracic or 
abdominal surgery; (3) no previous history of respiratory problems.  
 
The exclusion criteria are: (1) acute myocardial infarction or acute heart failure; (2) 
acute pain in the chest or abdominal; (3) with the clinical signs of significant pulmonary 
disease; (4) unstable hypertension, arrhythmias, or unstable cardiovascular conditions, 
such as fluctuations in blood pressure and heart rate, indicate poor cardiac prognosis or 
the need for vasopressor medications; (5) pregnant. 
 
Ethical approval: 
Ethical approval will be sought from the Research Ethics Committee of Hong Kong 
Metropolitan University and Shenzhen Second People’s Hospital. 
 
Sample size calculation: 
Sample size calculation will be based on the use of repeated-measures analysis of 
variance (ANOVA) using the G*Power 3.1. Considering an effect size of 0.2, an alpha 
error probability of 0.05 and a power of 0.80, the estimated sample size is 54 
participants. An additional 20% of the sample size will be included to account for 
attrition. The final estimated sample size will be at least 130 participants (65 for each 
cohort). 
 
Procedure: 
The nature of the study will be explained to the participants and written informed 
consent will be obtained. Demographic data of each participant including age, sex, 
height, weight, BMI, percent body fat, lean body mass, and smoking history will be 
recorded. For people after stroke, the stroke type (cerebral infarction, intracerebral 
hemorrhage), medical history (hypertension, diabetes mellitus, cardiovascular disease, 
lipidemia, kidney disease) will also be recorded. The National Institutes of Health 
Stroke Scale (NIHSS), Modified Rivermead Mobility Index (MRMI), Modified Rankin 
Scale (mRS), Barthel index (BI) will be retrieved from the patient’s medical record. 
 
Participants will be invited to attend the cardiopulmonary laboratory of the hospital at 
a time > 2 hours after a light meal. Participants are requested to avoid caffeine-
containing products, nicotine, alcohol and vigorous exercise for at least 12 hours before 
attending the laboratory. 
 
Each participant will be asked to perform the lung function test to measure the FVC, 
FEV1, and MIP after including the study. After completing the baseline lung function 
test, participant will be required to sit on the chair and rest for 15 minutes, after that, 
two trained researchers will use two identical ultrasonography to measure the left and 
right diaphragmatic thickness simultaneously at quiet breathing, the end of tidal 
inspiratory and the end of tidal expiratory, respectively. 3 ultrasonic images will be 
captured to calculate the mean diaphragmatic thickness of each breathing status. In 
order to determine the inter-rater reliability of the measurement of ultrasonography of 

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those two trained researchers, 20 participants will be chosen out randomly to receive 
twice diaphragmatic thickness measurement at quiet breathing, the end of tidal 
inspiratory and the end of tidal expiratory. However, during the second measurement, 
those two trained researchers will change their position to measure the contralateral side 
diaphragmatic thickness independently. 
 
After the baseline measurement, all participants will be requested to use a nose clip to 
hold the nose and breathe with the mouth through a pressure threshold inspiratory 
loading device (POWERbreathe, KH2, England). The inspiratory pressure will be set 
at 30%, 40%, 50%, 60%, 70%, or 80% of their MIP, in random order. Each MIP 
intensity protocol consists of 10 breaths. The procedure of IMT is followed by the 
published research protocols in people after stroke [28]. All MIP intensity protocols will 
be conducted in one day. A period of at least 10 minutes of rest time will be allowed 
between different protocols of contraction intensity (% MIP) on the same day [29].  
 
Thickness of the left and right diaphragm (stroke and non-stroke), will be measured 
simultaneously by two identical ultrasonography at the end of maximum inspiration of 
10 breaths of each MIP intensity protocol. The diaphragm thickness of both the left and 
right diaphragm at the end inspiratory breaths of the 10 breaths of each MIP intensity 
protocol will be recorded. Surface electromyography (sEMG) will be used to measure 
the activity of accessory muscle (sternocleidomastoid muscles) during each MIP 
intensity protocol. The % of MIP that associates with the highest calculated DTF and a 
relatively stable change in the activity of accessory muscles will be considered an 
appropriate training intensity for further IMT protocols. 
The self-perceived exertion level will also be determined by the Rate of Perceived 
Exertion Borg scale at the end of each MIP intensity protocol [30].   
 
All research procedures will be repeated again after 2 days to examine the test-retest 
reliability of ultrasonographic measurements of DTF. 
 
Outcome measures: 
Lung function  
FVC, FEV1 will be measured by using a spirometer (XEEK, X1, China), MIP will be 
measured by another device (Power Breathe, KH2, England). During the lung function 
tests, participants need to remain in the upright sitting position with a nose clip that 
tightly fits the nostrils. To record MIP, participants will be instructed to perform 
inspirations against an obstructed airway within the mouthpiece at near-residual volume. 
All lung function tests require each participant to inhale and exhale as hard and as fast 
as possible, then complete the cycle by inspiring as hard and rapidly as possible. Each 
test will be required to be performed at least three times, with each test not differing by 
more than 5% or 100 milliliters. The largest value obtained from the three executions 
will be used in the final analysis [31]. All tests will follow the recommendations 
proposed by the guidelines of the lung function tests [32].  
 
Power Breathe (KH2) 
The Power Breathe KH2 is an inspiratory muscle training device designed to improve 
the strength and endurance of inspiratory muscles (as shown in picture 1) [33]. It 
consists of a mouthpiece and a breathing valve. The valve is calibrated to provide a 
specific resistance during inhalation. The resistance can be adjusted on the device 
according to the IMT prescription. Participant needs to inhale through the mouthpiece 

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and drive their inspiratory muscle to contract against the external inspiratory breathing 
load.  
 
 
  
    
     
 
 
  (a)                    (b)                    (c) 
 
(a) the lateral side of Power Breathe (KH2). 
(b) the front side of Power Breathe (KH2). 
(c) the back side of Power Breathe (KH2), the top part (blue color) is the breathing 
valve.  
 
Muscle activity of sternocleidomastoid muscles  
Surface electromyography (sEMG) (Telemyo 900 from Noraxon USA) will be used to 
measure accessory inspiratory muscle (sternocleidomastoid muscles) activity during 
each MIP intensity protocol. The electrodes for sEMG will be attached to the bilateral 
sternocleidomastoid muscles (SCM). The locations of the electrodes will be placed at 
the mid-point of the left and right SCM muscles to measure the muscle activity of IM 
(shown in figure 1(a)). The sEMG responses will be amplified (gain × 1,000); the band-
pass will be filtered between 5 and 500 Hz, and digitized at a sampling rate of 1 kHz 
by using an analogue to-digital converter. The acquired data will be later analyzed using 
matching software. 
 
The measurement of diaphragmatic thickness 
Diaphragmatic thickness will be measured by the ultrasound machine (Mindray 9, 
Shenzhen, PRC). Ultrasonography is a portable, noninvasive emerging technique 
allowing easy and rapid estimation of muscle thickness [34, 35]. It not only can avoid 
the risk of exposure to radiation in medical facilities but also the reliability in providing 
a clear visualization of the muscle morphology at the zone of apposition [35, 36]. 
 
For consistency, all measurements will be conducted using the same transducer probe 
(model SuperLinear SL18-8; SuperSonic Imagine) with a bandwidth of 5 -18Hz of B 
mode. Ultrasonography will be performed by two trained physiotherapist who operates 
the machine under the guidance of a radiologist who is trained to use diagnostic 
ultrasound. 
 
Participant needs to remain in the upright sitting position on the chair during the 
measurement procedure. To measure the right diaphragmatic thickness, the transducer 
probe will be placed in the right intercostal space above the eighth or ninth intercostal 
space, between the antero-axillary and mid-axillary lines with a 45° angle tilt between 

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the surface of the abdominal wall in the cephalic direction, where the diaphragm is most 
suitable visualized (shown in figure1(a)). To measure the left diaphragmatic thickness, 
the transducer will be placed in the left intercostal space above the eighth or ninth 
intercostal space, between the anterior subcostal region between the anterior and 
midaxillary lines (shown in figure 2(a)). The diaphragm is observed as a three-layered 
structure, with the hypoechogenic muscular layer bordered by echogenic layers—the 
peritoneum and the diaphragmatic pleurae (as shown in figure2(b) and figure2(c)). 
 
Figure 1 The placement of transducer probes, surface electromyography electrodes and 
image of the diaphragm  
 
 
                                                                  
 
(a) The placement of transducer probes when measure of the right and left diaphragm 
by ultrasonography in people after stroke (left hemiplegia); The blue points represent 
the locations of surface electromyography electrodes on the sternocleidomastoid 
muscles. 
  
      
(b) Diaphragmatic thickness images of the left diaphragm (stroke side) at the end of 
tidal expiration and the end of maximum inspiration at 30 %MIP. 
 

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(c) Diaphragmatic thickness images of the right diaphragm (non-stroke side) at the end 
of tidal expiration and the end of maximum inspiration at 30 %MIP. 
 
 
 
Research flow chart 
 
 
 
 
Reporting of adverse event: 
Though various measures will be taken to minimize the risk of adverse event throughout 
the study, any adverse events that might happen will be recorded. 
 
Statistical analysis: 
All data will be reported as mean ± standard deviation (SD) unless otherwise indicated. 
Demographic data and clinical characteristics for all participants will be summarized 
using descriptive statistics. Repeated-measures ANOVA will be used to compare the 
differences of DTF and sEMG parameters determined at each inspiratory pressure 
separately. Intraclass correlation coefficient will be used to determine the inter-rater 
reliability of two ultrasonic operators and examine the test-retest reliability coefficient 
of ultrasonographic measurements of DTF recorded with different inspiratory pressures. 

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P value will be set at 0.05. All data will be analyzed using the IBM SPSS Statistics for 
Windows, Version 25.0 (Armonk, NY: IBM Corp). 
 
References: 
1. Gbd, S., Global, regional, and national burden of stroke and its risk factors, 1990-
2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet 
Neurol, 2021. 20(10): p. 795-820. 
2. Wu, X., et al., The hospital costs of stroke patients in Chinese island populations: an 
11-year tendency analysis. J Stroke Cerebrovasc Dis, 2015. 24(5): p. 988-992. 
3. Feigin, V., et al., Global, Regional, and Country-Specific Lifetime Risks of Stroke, 
1990 and 2016. N Engl J Med, 2018. 379(25): p. 2429-2437. 
4. Li X and Z. X., Annual data set on national mortality surveillance 2018. Beijing: 
China Science and Technology Press, 2019. 
5. Menezes, K.K., et al., Respiratory muscle training increases respiratory muscle 
strength and reduces respiratory complications after stroke: a systematic review. J 
PHYSIOTHER, 2016. 62(3): p. 138-44. 
6. Liu, X., et al., Assessment of Diaphragm in Hemiplegic Patients after Stroke with 
Ultrasound and Its Correlation of Extremity Motor and Balance Function. Brain 
Sciences, 2022. 12(7): p. 882. 
7. Lista-Paz, A., et al., Pulmonary function in patients with chronic stroke compared 
with a control group of healthy people matched by age and sex. Physiother Theory 
Pract, 2022: p. 1-9. 
8. Wilson, R., Mortality and cost of pneumonia after stroke for different risk groups. J 
Stroke Cerebrovasc Dis, 2012. 21(1): p. 61-67. 
9. Saposnik, G., et al., Variables associated with 7-day, 30-day, and 1-year fatality after 
ischemic stroke. Stroke, 2008. 39(8): p. 2318-2324. 
10.Koennecke, H., et al., Factors influencing in-hospital mortality and morbidity in 
patients treated on a stroke unit. Neurology, 2011. 77(10): p. 965-972. 
11.Dres, M., et al., Coexistence and Impact of Limb Muscle and Diaphragm Weakness 
at Time of Liberation from Mechanical Ventilation in Medical Intensive Care Unit 
Patients. AM J RESP CRIT CARE, 2017. 195(1): p. 57-66. 
12.Norisue, Y., et al., Association of Diaphragm Movement During Cough, as Assessed 
by Ultrasonography, With Extubation Outcome. RESP CARE, 2021. 66(11): p. 
1713-1719. 
13.Kim, M., et al., Diaphragm Thickness and Inspiratory Muscle Functions in Chronic 
Stroke Patients. Med Sci Monit, 2017. 23(null): p. 1247-1253. 
14.de Almeida, I.C., et al., Effects of hemiplegy on pulmonary function and 
diaphragmatic dome displacement. RESP PHYSIOL NEUROBI, 2011. 178(2): p. 
196-201. 
15.Lanini, B., et al., Chest wall kinematics in patients with hemiplegia. AM J RESP 
CRIT CARE, 2003. 168(1): p. 109-13. 
16.Sarwal, A., F. Walker, and M. Cartwright, Neuromuscular ultrasound for evaluation 
of the diaphragm. MUSCLE NERVE, 2013. 47(3): p. 319-329. 
17.Jung, J. and N. Kim, The correlation between diaphragm thickness, diaphragmatic 
excursion, and pulmonary function in patients with chronic stroke. J PHYS THER 
SCI, 2017. 29(12): p. 2176-2179. 
18.Enright, S., et al., Effect of high-intensity inspiratory muscle training on lung 
volumes, diaphragm thickness, and exercise capacity in subjects who are healthy. 
PHYS THER REHABIL J, 2006. 86(3): p. 345-354. 

Version 1. 12/29/2023 
 
9 
 
19.Inzelberg, R., et al., Inspiratory muscle training and the perception of dyspnea in 
Parkinson's disease. CAN J NEUROL SCI, 2005. 32(2): p. 213-217. 
20.Kodric, M., et al., Inspiratory muscle training for diaphragm dysfunction after 
cardiac surgery. J THORAC CARDIOV SUR, 2013. 145(3): p. 819-823. 
21.Lee, C., et al., Inspiratory muscle activation during inspiratory muscle training in 
patients with COPD. RESP MED, 2021. 190(null): p. 106676. 
22.Gomes-Neto, M., et al., Effects of Respiratory Muscle Training on Respiratory 
Function, Respiratory Muscle Strength, and Exercise Tolerance in Patients 
Poststroke: A Systematic Review With Meta-Analysis. ARCH PHYS MED REHAB, 
2016. 97(11): p. 1994-2001. 
23.Fabero-Garrido, R., et al., Respiratory muscle training improves exercise tolerance 
and respiratory muscle function/structure post-stroke at short term: A systematic 
review and meta-analysis Inspiratory muscle training for the recovery of function 
after stroke. ANN PHYS REHABIL MED, 2021. 65(5): p. 101596. 
24.Jung, J. and N. Kim, The effect of progressive high-intensity inspiratory muscle 
training and fixed high-intensity inspiratory muscle training on the asymmetry of 
diaphragm thickness in stroke patients. J PHYS THER SCI, 2015. 27(10): p. 3267-
3269. 
25.Parthasarathy, S., et al., Sternomastoid, rib cage, and expiratory muscle activity 
during weaning failure. J APPL PHYSIOL, 2007. 103(1): p. 140-7. 
26.Jung, J.H. and N.S. Kim, Relative activity of respiratory muscles during prescribed 
inspiratory muscle training in healthy people. J PHYS THER SCI, 2016. 28(3): p. 
1046-9. 
27.Breslin, E.H., et al., Correlations between dyspnea, diaphragm and sternomastoid 
recruitment during inspiratory resistance breathing in normal subjects. CHEST, 
1990. 98(2): p. 298-302. 
28. Lee Kyeongbong, Park Daesung, Lee GyuChang. Progressive Respiratory Muscle 
Training for Improving Trunk Stability in Chronic Stroke Survivors: A Pilot    
Randomized 
Controlled 
Trial. 
Journal 
of 
Stroke 
& 
Cerebrovascular   
Diseases.2019;28 (5)：1200-1211. 
29.Ramsook Andrew H, Koo Ryan, Molgat-Seon Yannick, et al. Diaphragm Recruitment 
Increases during a Bout of Targeted Inspiratory Muscle Training. MEDICINE AND 
SCIENCE IN SPORTS AND EXERCISE.2016;48 (6):1179-86. 
30.Borg G A. Psychophysical bases of perceived exertion. MEDICINE AND SCIENCE 
IN SPORTS AND EXERCISE.1982;14 (5):377-81. 
31.Society AT. ATS/ERS statement on respiratory muscle testing. Am J Respir Crit Care 
Med. 2002; 166:518–624. 
32.Neder JA, Andreoni S, Lerario MC, Nery LE. Reference values for lung function 
tests. II: maximal respiratory pressures and voluntary ventilation. Braz J Med Biol 
Res 1999; 32: 719-27. 
33. Nepomuceno Júnior, Balbino Rivail Ventura, Thaís Borges Gómez, and Mansueto 
Gomes Neto. "Use of Powerbreathe® in inspiratory muscle training for athletes: 
systematic review." Fisioterapia em Movimento 29 (2016): 821-830. 
34.DiNino E, Gartman E, Sethi J, McCool F. Diaphragm ultrasound as a predictor of 
successful extubation from mechanical ventilation. Thorax. 2014;69(5):423-7.  
35.Nakanishi Nobuto, Oto Jun, Ueno Yoshitoyo, et al.Change in diaphragm and 
intercostal muscle thickness in mechanically ventilated patients: a prospective 
observational ultrasonography study.Journal of intensive care.2019;7：56. 

Version 1. 12/29/2023 
 
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36.Boussuges A, Gole Y, Blanc P. Diaphragmatic motion studied by m-mode 
ultrasonography: 
methods, 
reproducibility, 
and 
normal 
values. 
Chest. 
2009;135(2):391-400.