It is evident from the results that the use of the jacket as assistance for inspiration and expiration reduces the effort and number of trials required in conducting the FVC manoeuvre. The change in the values of the variables was insignificant, but once a similar study is conducted with a greater number of participants, the results will be more conclusive. Hence, specific investigations along the line of PFT requirements will result in the proper and specific use of this jacket. Furthermore, implementation of the following discussed suggestions may replace or aid body-box plethysmography with jacket plethysmography.
Considering the background of this study, many questions emerge that we have tried to answer.
Q1. In clinical practice, we use lung function testing to observe the patient's ability to move air, assessing both neuromuscular function and lung function together. What would be the point of adding artificial mechanical assistance to perform spirometry?
Ans: As explained in the introduction, the FVC manoeuvre is not easy for every patient to perform; even with the patient’s ability, it is often not performed properly or with full effort. Hence, proper coordination of this response (gasp and assisted expiration using the jacket) will help reduce the effort required of the patient and will also decrease the number of attempts required to obtain the desired and acceptable manoeuvre.
Additionally, the advanced design suggested in the supplementary information (please refer to the file ‘Design and Calculations’) proposes that the forced expiration would be proportional to the inspiratory efforts. Thus, by mimicking the physiology of forceful expiration, the doubt of confounders in interpreting PFT results can be eliminated, with the additional benefit of measuring residual volume.
Q2. Why are all the subjects male, and why is the sample size small?
Ans: The jacket requires multiple people to operate, and the fact that a bare chest is required limits its use on female participants. Additionally, as explained above, this is a pilot project whose aim is to automate spirometry manoeuvres. Hence, to prove this concept with a minimalistic approach, we proceeded with healthy males only.
Furthermore, definitive investigative studies regarding the jacket’s suggested advancements and its use in different age groups, types of diseases and sexes are needed.
Q3. Why is cold water at a temperature of 10°C used for the procedure, and what is the ideal temperature for gasp response?
Ans: The water temperature that comes in direct contact with the body should be 10°C because at this temperature, the gasp response is maximal. This gasp is equivalent to the vital capacity (at 26°C, the gasp response is approximately 2 litres, while at 10°C, it is approximately 3 litres)6,7.
Q4. What are the dimensions and distributions of the cold receptors?
Ans: Cold receptors are small spots on the nerve endings that are densely distributed in the upper torso region8.
Q5. What are the alternative sources for cold stimulation?
Ans: The following alternative sources can be used for cold stimulation:
Peltier thermode – An electric device used to generate cold stimulation. This alternative is an expensive method, and its ability to reach the desired temperature is very slow.
Cool air – The rate of heat transfer from the body using cool air is 25% less than that of water.
Liquid nitrogen – This alternative is effective but not advisable since accidental leakage can cause severe health hazards.
Q6. What should be the duration of exposure for the inspiratory phase and expiratory phase?
Ans: Inspiratory cold shock and expiratory pressurization are maintained manually in the PFT induction jacket, i.e., cold shock is administered with the start of inspiration for 2 seconds, while chest compression is administered with expiration for 4 seconds.
The results can be improved if the above protocol is controlled and executed by computer software with prior and proper knowledge of the time parameters in ventilation1.
Q7. How much external pressure is required for assisted expiration?
Ans: According to the tank respirator reference, there is a need for only + 5 cm of H2O to obtain assisted expiration9. However, in our jacket, we used 70–80 psi (4921.49-5624.56 cm of H2O) for effective circumscribing pressure in the jacket. The reason for such a high-pressure requirement is that the jacket has a very thin and malleable outer layer, which leads to ballooning; hence, most of the pressure is dissipated on the outer side of the jacket.
In an advanced jacket, a pressure release valve can be fitted into the jacket for additional safety. We also suggest the addition of pressure sensors in the jacket, which sense the pressure in the jacket before the start of inspiration and at the end of the inspiratory gasp. This raised end inspiratory pressure in the jacket should be maintained throughout the assisted expiration (application of Boyle’s law as performed in body-box plethysmography; please refer to the file ‘Design and Calculations’ in the supplementary information).
Q8. What is the weight of the device? Is there any effect of this weight on the pulmonary function test?
Ans: The weight of the device is 1.81 kg (4 lb) without active flow and 2.95 kg (6.5 lb) with active flow.
Many studies have reported the impairment of respiratory functions with external weight. For example, a study by Collins et al.10 showed the effect of body fat distribution on pulmonary function tests. Studies by Marabotti et al.11 and Schellart and Sterk12 show the effect of a wetsuit on respiratory functions.
With reference to the advancement suggested in Question 9, the impairment of respiratory functions due to weight can be minimized.
Q9. What will be the effects of induced assisted respiration on the flow-volume curves of a participant?
Ans: For any given individual during expiration, there is a unique limit to the maximal flow that can be reached at any lung volume. This limit is reached with moderate expiratory efforts, and increasing the force exerted during expiration does not increase the flow1.
This can be understood by a simple example where we suppose that the lung is contained in a thorax whose volume can be changed by a piston. The piston is formed by the respiratory muscles, which helps create negative pressure and positive pressure for inspiration and expiration, respectively. Because the lungs are elastic, they drive the flow and play a vital role in holding the compliant bronchi open even during critical narrowing during forced expiration. In our case, the jacket plays the part of the piston. Provided that the participant has no neuromuscular disorder, this induced assisted respiration via the jacket will mimic the physiological pattern and lead to better results.
Additionally, regarding the pressure management suggested in Question 7, we also suggest that the jacket can be divided into three main parts, each of which can be further divided into anterior and posterior segments (please refer to the file ‘Design and Calculations’ in the supplementary information). One part can cover the abdomen, and the other two can cover the lower and upper chest. The purpose is to provide successive compression starting from the abdomen and moving through the lower thorax and the upper thorax, which may minimize the issue of critical narrowing. However, additional investigations are required to prove this hypothesis. The segments can be suspended using a sliding stand, which can help split the weight of the jacket.
The benefit of the three-part design would be in the use of the jacket; the subject can sit in the middle, and the segments on the stand can be moved to be in contact with the body, i.e., the body can be sandwiched between the segments. By doing so, apart from reducing the duration of the procedure, the cumbersome way to put on and take off the jacket, as shown in the video clip, can also be eliminated.
Q10. What will be the repeatability of the response?
Ans: Humans are highly adaptable. With repeated exposure, the body becomes habituated to cold stress; for example, exposure to cold water for as short a time as three minutes in a 10 minute shower will attenuate the cold-shock response by as much as 20–30%13,14.
Q11. What are the emergency problems associated with the use of cold shock and external pressure?
Ans: Respiratory responses to cold water immersion have been well covered by Datta and Tipton6. This study reported that immersion of an unprotected body in cold water produces a large and rapid fall in skin temperature, which, in turn, evokes the initial responses to cold immersion, given the generic name “cold shock”. The response comprises inspiratory gasp, hypertension, and hyperventilation. Additionally, neuronal mechanisms suggest that, apart from anticipatory anxiety, cold shock may result in cardiac arrhythmias and cardiac arrest in susceptible individuals, such as those with long QT syndrome.
This setup is a simulation of only the initial part of the cold shock. That is, the participant, breathing freely (without holding their breath), is exposed to cold water for only a few seconds without being immersed, which is associated with the initial physiological effects of cold shock. However, there should be an emergency kit comprising antihypertensives, antiarrhythmic drugs, and defibrillators present in proximity. Since there is only momentary exposure to cutaneous cold stimulation, the abovementioned complications are much less likely to develop. This is also supported by the poor evidence of complications at such a low dose of exposure6.
The complications of external pressure administered by mechanical chest compression devices during cardiopulmonary resuscitation include skin or skeletal injury and even life-threatening complications, such as mediastinal bleeding and injuries of the heart, aorta, lung, liver, spleen and stomach15.
However, in our jacket, the compression elicited can be compared with the compressions generated by high-frequency chest wall compression (HFCC) devices16. These devices are vests that are connected with two tubes to an air-pulse generator, which inflate the vest with a constant positive pressure with a 15–20 Hz frequency of air pressure oscillations. These devices are used as portable mechanical methods of self-administered chest physiotherapy, often required for assisting mainly cystic fibrosis patients with expectorating dislodged bronchial secretions while actively huffing and coughing intermittently during use17–19. Our jacket provides chest compression with the intention to assist with a single expiration.
Nevertheless, a question arises regarding the safety of the jacket’s use in a patient with emphysema who has air trapping. Only definitive investigation of its use among such patients can determine the amount and pattern of permissible pressure required to assist expiration. The jacket can be a useful tool for inducing gasps, e.g., half of the manoeuvre can be automated; for the second half of the manoeuvre, the jacket should be used with caution.
In our present study, no complications or catastrophic events were observed.
Q12. How much time was required to perform spirometry using the jacket?
Ans: Spirometry took ~ 20–25 min for each participant to perform, which is clearly more time-consuming than the conventional method. However, by implementing the suggestion in Question 9, the operational difficulties in the use of the jacket can also be minimized.
Q13. What kind of material should be used for the jacket?
Ans: For the inner and middle layers, the material should be durable, malleable and a good conductor of heat. The material must be washable or sterilizable.
For the outer layer, a tough and lightweight material can be used (such as the material used in suitcases).
Q14. How can the jacket be sealed at various places, such as the arms, abdomen, and neck?
Ans: Any flexible and airtight collar can be used for this purpose, as attempted by Bruggink et al.20 for leak-free head-out plethysmography in mice. Since an advanced technique is required to achieve this feat, the present device does not have this setup.
Q15. How can the results be improved?
Ans: Computer software, which can better sync the delivery of cold shock and assisted expiration with the patient’s breathing pattern, can increase the accuracy (also mentioned in Question 6). Using software can remove the need for manual delivery, which requires perfect coordination among multiple staff to achieve.
Application of the other suggested advancements can also aid in improving the results. In this article, we are more focused on advocating the concept rather than the results.
Q16. What are the advantages and disadvantages of the jacket?
Ans: After discussions with the patients, doctors, and technicians, we decided to make modifications based on the advantages and disadvantages mentioned in Table 3.
Table 3
Advantages and disadvantages with the jacket and without the jacket
| Spirometry without jacket (conventional way) | Spirometry with jacket |
Advantages | • No gender bias. | • Saves time by aiding the manoeuvre. • Effort for training of the patients reduced. • Reduced number of attempts to perform the acceptable manoeuvre will allow for investigation of more patients in less time. • Reduces patient effort-related errors in the report. • Aiding stimuli are purely physiological. |
Disadvantages | • Time-consuming due to many initial weak efforts, especially by noncompliant patients. • Too many attempts may cause fatigue and reduced efforts during the manoeuvre. | • Needs further research in different age groups, genders, and diseases before using it for diagnosis. • Emergency kit should be available to deal with cold stimulus-related responses, if any. |
Q17. Is there a possibility for advancement in the jacket?
Ans: Since the patent was granted, the commercialisation gates have been opened, which expands the scope. With advanced design and materials (as suggested in Questions 7, 9, 13, 14, and 15 and in supplementary information; Design and Calculations), the jacket is potentially able to convert full-body plethysmography to jacket plethysmography. This provides additional benefits of better compliance and cost effectiveness for the patients.
Therefore, we can conclude that this invention is based on a unique concept that can help reduce the number of voluntary efforts of patients undergoing pulmonary function tests (PFTs). It will not only assist the patients but will also reduce the trial, time, and energy of the medical practitioner in teaching the manoeuvre to the patients. Additionally, with further advancements in the jacket, it has the capability to convert body-box plethysmography to jacket plethysmography.