Non-Invasive Assessment of Abdominal/Diaphragmatic and Thoracic/Intercostal Spontaneous Breathing Contributions

Abstract

(1) Background: Technically, a simple, inexpensive, and non-invasive method of ascertaining volume changes in thoracic and abdominal cavities are required to expedite the development and validation of pulmonary mechanics models. Clinically, this measure enables the real-time monitoring of muscular recruitment patterns and breathing effort. Thus, it has the potential, for example, to help differentiate between respiratory disease and dysfunctional breathing, which otherwise can present with similar symptoms such as breath rate. Current automatic methods of measuring chest expansion are invasive, intrusive, and/or difficult to conduct in conjunction with pulmonary function testing (spontaneous breathing pressure and flow measurements). (2) Methods: A tape measure and rotary encoder band system developed by the authors was used to directly measure changes in thoracic and abdominal circumferences without the calibration required for analogous strain-gauge-based or image processing solutions. (3) Results: Using scaling factors from the literature allowed for the conversion of thoracic and abdominal motion to lung volume, combining motion measurements correlated to flow-based measured tidal volume (normalised by subject weight) with R² = 0.79 in data from 29 healthy adult subjects during panting, normal, and deep breathing at 0 cmH₂O (ZEEP), 4 cmH₂O, and 8 cmH₂O PEEP (positive end-expiratory pressure). However, the correlation for individual subjects is substantially higher, indicating size and other physiological differences should be accounted for in scaling. The pattern of abdominal and chest expansion was captured, allowing for the analysis of muscular recruitment patterns over different breathing modes and the differentiation of active and passive modes. (4) Conclusions: The method and measuring device(s) enable the validation of patient-specific lung mechanics models and accurately elucidate diaphragmatic-driven volume changes due to intercostal/chest-wall muscular recruitment and elastic recoil.

Keywords: abdominal; circumference; monitoring; muscular recruitment; respiratory mechanics; rotary encoder; thoracic.

Figure 1

Breath-wise peak chest and abdominal circumferential changes (mm) against tidal volume (L). For men and women breathing normally, deeply, and panting at ZEEP, 4, and 8 cmH₂O CPAP-set PEEP.

Figure 2

Breath-wise scaled sum of peak circumferential changes in chest and abdomen (mm) against tidal volume normalised by subject weight (L/kg). For men and women breathing normally, deeply, and panting at ZEEP, 4, and 8 cmH₂O CPAP-set PEEP.

Figure 3

Breath-wise scaled sum of peak circumferential changes in thorax and abdomen (mm) against tidal volume normalised by subject weight (L/kg). For men and women breathing normally, deeply, and panting at ZEEP, 4, and 8 cmH₂O CPAP-set PEEP.

Figure 4

Breath-wise scaled sum of peak circumferential changes in thorax and abdomen (mm) against tidal volume normalised by subject weight (L/kg). For subjects breathing normally, deeply, and panting at ZEEP, 4, and 8 cmH₂O CPAP-set PEEP. Separated by men and women (a), asthmatics and non-asthmatics (b), vapers and non-vapers (c), and smokers and non-smokers (d).

Figure 5

Breath-wise scaled sum of peak circumferential changes in thorax and abdomen (mm) against tidal volume normalised by subject weight (L/kg), separated by subject.

Figure 6

Chest and abdominal expansions (mm) over time (s) during normal breathing at ZEEP by subject.

Figure 7

Chest and abdominal expansions (mm) over time (s) during deep breathing at ZEEP by subject.

Figure 8

Chest and abdominal expansions (mm) over time (s) during panting at ZEEP by subject.

Figure 9

Subject 3 mean normal, deep, and panting breaths at ZEEP (against time (s)).

Figure 10

Subject 3 mean normal, deep, and panting breaths at 4 cmH₂O (against time (s)).

Figure 11

Subject 3 mean normal, deep, and panting breaths at 8 cmH₂O (against time (s)).

Figure 12

Subject 3 mean breath chest vs. abdominal expansions (mm).

Figure 13

Median subject ratios of peak abdominal-to-chest motion over PEEP for normal breathing (outliers above 10 times abdominal-to-chest peak expansion are not shown for clarity).

Figure 14

Median subject ratios of peak abdominal-to-chest motion over PEEP for deep breathing (outliers above 10 times abdominal-to-chest peak expansion are not shown for clarity).

Figure 15

Median subject ratios of peak abdominal-to-chest motion over PEEP -for panting (outliers above 10 times abdominal-to-chest peak expansion are not shown for clarity).