Determination of Dyspnea: Sensation Dynamics and Inspiratory Resistance Detection

This study aims to determine the effects of three dynamics on the sensation of dyspnea and inspiratory load detection, thus investigating the threshold of the latter as a trigger for breathlessness.  The determinants namely cardiorespiratory fitness (CRF), body characteristics and lung function are vital in uncovering several novel findings as presented within this study.  Some of these results indicate anomalies which occurred from external conditions during the study.  Such defects will help us further determine whether there is a relationship between the three factors and their role in the level of sensation of dyspnea.

  Firstly, participants with lower VO2max demonstrated reduced dyspnea sensation.  Inspiratory load detection does not accompany such observation.  Secondly, a lower FEV1 resulted in a higher severity of breathlessness (with no relation to inspiratory load detection) and lastly, the smaller the MIP (maximal inspiratory pressure), the higher the severity of breathlessness.  These findings suggest that low cardiorespiratory fitness and reduced lung function affect the severity of dyspnea sensation(Kauffman et al.,2014).  Since ideal results cannot be attained due to physiological differences, specific measures were implemented to ensure that data obtained conformed to a pattern that could be interpreted easily

The probability of developing breathlessness due to any obstruction intrinsic or otherwise in this study, accompanied by any pulmonary or respiratory malfunction is excluded since participants are healthy.  An increase in inspiratory pressure was not due to a decrease in inspiratory airflow because the inspiratory pressure was carefully relativized to the airflow rate that the participants inspired.  Therefore efforts made by participants inspiratory-wise were eliminated.  It is well known for inspiratory pressure to increase and inspiratory airflow to decrease while adding resistive loads to the inspiration which induce the respiratory effort to expand and breathlessness to develop (Kifle et al., 1997).  As a result, there is a substantial decrease in the mechanical load stimulus (afferent information) and correspondingly increases the inspiratory load detection (Killian, 1981).  It, therefore, interprets what was confirmed according to the mechanism of breathlessness that could occur when there was a mismatch between perceptual inspiratory detection or awareness and afferent information during inspiratory loading (Schwartzstein et al., 1989).  Several different factors become vital in understanding this mismatch.  These factors are counterchecked against previous literature and findings on similar studies to determine their cause.  One such element is the methodology used to measure the minimum mechanical burden added and perceptual awareness detection.

In this study, the measurement of respiratory sensation would chiefly be gauged by the least mechanical load added. Theoretically, it would mean comparing ratings of breathlessness from three clinical scales in respect to the appended pressures. This aspect is resistive in type and inefficient. This was unlike some previous investigations which focused on psychophysics of respiratory perception (Zichman& Wiley, 1986).  Perceptual awareness and load detection have also been studied using a method that involves magnitude inspiratory airflow, inspiratory pressure, and frequency, similar to previous studies (Kifle et al., 1997).  While an increase in the threshold of inspiratory load detection was well known within a clinical population in affecting the ability to detect inspiratory pressures, the cause of decreased inspiratory load detection and perceptual awareness was still unknown (Kifle et al., 1997).  After considering these factors, it was easier and accurate to come up with control measures to ensure that the anomaly observed was eliminated and observations made.

  Therefore, this study highlighted the detecting changes of inspiratory load (ChP) beside threshold of inspiratory load detection (ThP), in addition to the sensations of breathlessness, after considering all ideal variables.  Also, this study found a correlation between the three independent variables namely CRF, body characteristics and lung function to its findings.  Progression of each reliant variable can be seen in appendix 9 indicating all trials of different resistive loads.  This data also clarifies the comparison among all participants.  It was concluded that the dependent variables measured in this study, namely inspiratory pressures (IP), the threshold of inspiratory load detection (ThP), time of limit of inspiratory load detection and detecting changes of inspiratory loads (ChP) acted healthily.  Such behavior comes after considering the difference in participants both physiologically and psychologically.  The data hence shows a slight fluctuation as expected.  In general, the data makes physiological sense and can be interpreted further from simple deduction and analysis.

The emotions of the participants or proper mouthpiece handling were factored in to explain the unusually high inspiratory pressures recorded from lower resistive loads.  In some participants, high pressures were recorded during baseline indicating a failure to inspire at the lower pressures.  However, this was followed by improvements as they had matched an increased inspiratory pressure with adding inspiratory resistive loads over the subsequent trials.  One explanation for this is panic experienced by the participants.  A significant variance was observed in these results from 31 participants.  The variance in data, however, can be explained by the fact that all participants were different, and that the breadth of data may only reflect the physiological and psychological variation found in a group of average (non-clinical) participants.  The physical contrast among the participants creates a spectrum from which one can observe how each of the three factors take effect in determining detection and sensation of dyspnea when an increase in resistive load is undertaken.  Figure four shows a regular pattern of progression (gain) in inspiratory pressures recorded, both absolute and relativized to airflow ratio, as the resistive loads were added continually (linear relationship) during the experiment.  Participants were inspired at lower magnitudes of inspiratory pressures starting from baseline until reaching maximal inspiratory pressures at resistive load six.  Absolute values of ThP increased albeit with a fluctuating pattern across the different intensities.  During the sixth trial, however, the recordings increased at the maximal resistive load.  On the other hand, during inspiratory loading, the relative ThP to airflow ratios decreased through the experiment indicating that as the resistive loads increased, participants got much better in inspiratory load detection.  Some variables of breathlessness, rated by participants, were raised along with inspiratory pressures (IP), recorded while adding resistive loads to inspiration.

Maximal inspiratory pressure

 A higher Maximal inspiratory pressure (MIP) translated to a lower breathlessness factor in lower resistive loads.  Such occurrence meant that individuals with such experience a reduced severity of dyspnea.  On the other hand, MIP correlated negatively to the threshold of inspiratory load detection (ThP) in high resistive loads (inspiratory pressures). Here participants with a higher MIP were detecting lower inspiratory pressure and demonstrated a lower threshold of inspiratory load detection (ThP), indicating a high ability to identify dyspnea and inspiratory loads.  It is also important to note that the physiological differences come to play when calculating MIP.  For example, age and sex could influence MIP and MEP values; these are lower in females than in males and quite constant until seventy years of age when they start to decrease(Terzano, 2006, p. 666-667).  These findings indicate that there are adequate respiratory function and ventilatory response because of the able diaphragm and inspiratory muscles as a result of high MIP, Ringqvist T (1966), the more upper inspiratory loads’ detection and less severity of dyspnea sensation.  This finding confirms those of a recent study (Patessio et al., 2017).  Despite the uniform pattern in the data, there was an unusual result.  The MIP correlated at baseline with the intensity of breathlessness.  As with other variables, this may be explained by participants not being comfortable during this initial phase of the tests.

FEV1

In this study, no significant relationship between FEV1 and threshold of inspiratory load detection (ThP) or detecting changes of inspiratory load (ChP) were found.  However, a correlation was evident between FEV1 and breathlessness whereby poor FEV1 was related to a high sensation of breathlessness. In a practical sense, most of the obstructive respiratory diseases associated with dyspnea are defined by a low FEV1.  Similar to this finding regarding Borg scale of breathlessness, a previous experimental study (Webb & O’Donnell, 1995) in asthmatic patients found that decreased FEV1 provoked the sensation of breathlessness.  These findings are also consistent in obese populations (Schachter et al., 2001; Zerah, 1993).

In the current study, the apparent correlation of FEV1 within sensation of breathlessness and the non-evident of its association with inspiratory load detection at the same time might raise questions behind the mechanism of breathlessness.  Also, the increase in the sensation of breathlessness among healthy participants who have efficient lung function was not due to any detectible obstructive disorders that should be reflected from universal values of FEV1 and FEV1/FVC of healthy subjects according to their body mass and age Allen J. (2017, Dec 5).  The differences in physical characteristics among the participants and their efforts applied during the test plus its impact on normative data can explain the unexpected variable outcomes of FEV1.  It, therefore, helps further in understanding dyspnea in the sense that it is more related to inspiratory loading in the airways rather than other contributing factors of awareness of breathing.  During the first resistive load trial the higher FEV1, the more significant threshold of inspiratory load detection (ThP) and hence low ability to detect dyspnea and inspiratory loads (lower inspiratory load detection).  Instances of familiarization and panic among participants at the beginning of the trial is a reasonable explanation for the anomaly.  A decreased FEV1 provokes the sensation of dyspnea, which can be explained by the exclusion of perceptual awareness.  No clear relationship between FEV1 and inspiratory load detection was observed among the healthy participants.  The effort caused by dyspnea and the value of FEV1 represent the level of lung function and further proves the existence of natural inspiratory obstruction among people.

CRF and dyspnea

A deduction of the data indicates that a higher level of CRF is common among participants due to the high VO2max.  These participants interpret as a better ability to sense breathlessness of all its different perceptions.  The same case was evident from baseline to the final trial (trial six).  There was no relationship between VO2max and variables of inspiratory load detection, ThP, and ChP.  These current findings do not conform to previous literature.  Instead, there is an apparent translation about the importance of training status and contributing to a high CRF level to reduce and prevent the sensation of breathlessness among healthy individuals (Perri et al., 2002; Ninot et al., 2007; Ortega et al., 2002).  However, another literature can explain this occurrence among participants who were measured with higher VO2max and experienced a high sensation of breathlessness.  It might be related to those people with high CRF using their higher proportion of their maximal ventilatorycapacity(Chang et al.,1999).  Breathlessness anxiety, which is a measure of dyspnea in this study, was correlated in a way that conforms to the current findings of the CRF (Faull et al., 2016).  Participants who experience high CRF and rated increased sensation of breathlessness might be aware of the high resistive loads when breathing during testing.  With this finding, one may argue that the outcomes agree with probability involving high sensitivity of breathlessness and is an advantage in clinical situations where poor sensitivity to inspiratory loading may present a risk to some asthmatic persons and delay medical interventions (Kifle et al., 1997).  Zechman, F., Wiley, R., & Davenport, P. (1981) also support this notion indicating how in patients with asthma, there is significant variability in the perception of added loads that does not correlate with age or measures of lung dysfunction.

Body characteristics and dyspnea

No significant relationship was observed between BMI and inspiratory load detection or sensation of dyspnea, a finding that agrees with previous literature. Those studies used participants with high BMI or obese as the main population in an experiment to test the efficiency of the lung function (Sahebjami, 1998; ERV; Jones, &Nzekwu, 2006).  A relationship was however found between BMI and reduction in lung function which can be explained by fat masses in the chest and abdomen areas instead of inspiratory loading or an increased BMI (Sahebjami, 1998; ERV; Jones, &Nzekwu, 2006).  Uncovering such a sentiment gives some explanation to why there was no significant connection between BMI and any variable regarding breathlessness and inspiratory load detection.  Jones, &Nzekwu, (2006) and Sharp et al. (1964) showed how obesity and BMI effects on lung functions among an obese population resulted from a restriction in the lung and movements of the diaphragm.During normal breathing, most of the respiratory work depends on the diaphragm function and the accessory respiratory muscles become necessary only during deep inspiration(Polla et al.,n.d.).The cause was determined to be thoracic and abdominal fats, measured by subscapular skinfold thickness (Lazarus, Sparrow & Weiss, 1997) and waist circumferences (Chen, Rennie, Cormier, &Dosman, 2007).

This finding can be explained by the range of BMI participants that were randomly nominated.  The scale used was between 20.00 and 39.60 with a mean value of 27.20.  A difference might be observed if other methods of assessing fat mass in this study were applied.  These include subscapular skin folds measurement and chest and waist circumferences.  No relationship was discovered between hip circumference, inspiratory load detection and the sensation of dyspnea.  This finding matched with the previous studies (ERV; Jones, &Nzekwu, 2006; Canoy et al., 2004) that stated no relationship of the thigh and hip fats to the reduced lung function and provoking respiratory symptoms such as breathlessness.(Gologanu, Ionita, Gartonea, Stanescu, &Bogdan, 2014) supports this notion.

Perspectives

Efforts to replicate the ideal baseline values of inspiratory pressure as determined in previous studies were in vain as the data showed variations.  These were contributed to by several factors that inflated inspiratory pressure.  For example, they slightly affected the length and diameter of the tube, and a pneumotachometer was used.  It was also unclear whether the measured pressure was absolute or not.  Although the inspiratory loads in the baseline achieved are not that typical comparing with previous studies, they were almost within the ranges of similar studies (Ruehland et al. 2016) that can be still in the region permitted for detecting the inspiratory loads and dyspnoea.  Further research might need to aim to lower the baseline pressure.  No observational differences, which represent actual differences and variability, can be observed within a limited number of patients in medical research (Biau, Kerneis, &Porcher, 2008).

Also, in this study, the breathing pattern which includes depth and frequency was not stabilized, and inspiration was not aimed during the test.  Instead, the inspiratory pressure was made relative to the airflow with the target of testing the participants in their normal breathing behavior.  Participants were asked to relax and breathe as usual as they can to achieve normality.  The intention here was to equalize the airflows of inspiration relative to the pressure hence eliminate the effect of different inspiratory efforts.  These efforts experienced during separate trials of the resistive load could affect the sensation of breathlessness.  Perceptual detection can also be affected by the rating on the scale while tending to press the trigger that represents ThP.  It may also be beneficial to study emotions and psychological status of participants to research if there are any relationships because mental characteristics such as anxiety and depression can affect the intensity of dyspnea intensity (Williams, Cafarella, Olds, Petkov&Frith, 2010).

 It is also possible that there was leakage of airflow out of the mouthpiece as the participants handled the measuring instrument themselves.  A decrease in the inspiratory pressure would be seen and thus affect the accuracy of the result.  Some countermeasures were implemented to that despite the minor setbacks the participants remained the same throughout the study.  Some confusion in observations in baseline and first resistive loads were found inconsistent with other main findings.  Inadequate familiarization sessions can probably explain why the participants experienced panic before getting adapted to the next resistive loads.  It might be helpful if they had practiced and familiarized with the range of loads.

Conclusion

The study therefore investigated and confirmed successfully how each of the factors affects dyspnea sensation and identification and further explained the anomaly of healthy persons experiencing a larger severity of breathlessness.  Evidently, the VO2max and MIP vary depending on the physiological profile of the participant and the training status.  Concluding this explains the mismatch in the relationship between CRF and dyspnea.  Lung function also plays a role in respiratory obstruction with the assistance of specific body characteristics like the effects of obesity.  However, no direct correlation is evident between body characteristics and any factor that provokes dyspnea sensation. Some smaller aspects of emotion and age play a role in determining the accuracy of this study.

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