The measurement of vital signs, such as heart and respiratory rates, is crucial for determining patient status (Brabrand, Hallas, Folkestad, Lautrup-Larsen, & Brodersen, 2018; Cahill et al., 2011). In recent years, attempts have been made to measure vital signs using noninvasive and noncontact methods (Bates & Zimlichman, 2015; Brown, Terrence, Vasquez, Bates, & Zimlichman, 2014). Respiratory status is determined by measuring respiratory rate and blood oxygen saturation; however, it is challenging to determine tidal volume by observing chest movement alone. In particular, for respiratory depression caused by the use of opioids and analgesics, using current technology, respiratory status can be determined using a mask or capnometer sensor (Frasca, Geraud, Charriere, Debaene, & Mimoz, 2015). However, wearing the device can be inconvenient. Therefore, noninvasive and noncontact methods that use new technology in measuring heart and respiratory rates and in determining changes in tidal volume are sought.
Purpose
This study aimed to examine the reliability and validity of methods used to measure changes in heart and respiratory rates and tidal volume using a novel noninvasive, noncontact biological information sensor.
Methods
The biological information sensor comprises a sensor sheet with an air-cell sheet structure, which uses a pyroelectric air-pressure sensor to detect minute movements caused by heart beat and respiration. Changes in heart and respiratory rates and tidal volume were measured according to the minute movements. The sensor was placed under a mattress on the operating table, making it noninvasive and noncontact for the patient. For heart and respiratory rates and tidal volume per breath, we used the PRO-NEXT+s anesthesia workstation (Acoma, Inc., Tokyo, Japan) and BSM 6701 bedside monitor (NIHON KOHDEN, Inc., Tokyo, Japan). We recorded the heart and respiratory rates and tidal volume per breath of the patients after induction of general anesthesia. Subsequently, we measured minute movements caused by heart beats and respiration using the sensor. Measurements were obtained for 3 hours (until surgery was completed).
Statistical Analysis
For the heart and respiratory rates measured using the biological information, we used a Bland–Altman plot to examine whether the difference between the two measurements was within 1.96 standard deviation (SD) (Giavarina, 2015) and whether the permissible range for the difference between the two measurements was ±5 beats/minute for heart rate and ±2 breaths/minute for respiratory rate ( Food and Drug Administration, 2007; Association for the Advancement of Medical Instrumentation, 2002;). Furthermore, the analysis was conducted using Lin’s concordance correlation coefficient (Lin, 1989). The correlation between changes in the ventilator volume per breath and minute movements caused by respiration was examined using Spearman’s rank correlation test. For all analyses, a p-value of <0.05 was considered statistically significant.
Results
Informed consent was obtained from the five patients who were enrolled in the study. Data obtained after induction of anesthesia and while moving the body during surgery were excluded. Bland–Altman analysis of heart and respiratory rates was performed, and these rates were measured using the biological information sensor. Results showed that the bias for heart rate and respiratory rate was 0.1 and 0.14, respectively, with bias SDs of 1.6 and 0.73, respectively, and 95% limits of agreement of −3.1 to +2.9 and −1.3 to +1.6, respectively. Lin’s concordance correlation coefficients for heart and respiratory rates were 0.968 and 0.966, respectively. Both results were within the permissible range at 5 beats/minute for heart rate and 2 breaths/minute for respiratory rate. Changes in tidal volume were then measured, and upon extracting 10 random points from one patient and calculating the surface area for inhaled and exhaled air, the correlation coefficient was 0.881. The correlation coefficient between changes in tidal volume measured using the anesthetic machine and the surface area during movement when inhaling and exhaling as calculated using the biological information sensor was 0.917.
Conclusion
Changes in heart and respiratory rates and tidal volume were measured using a noninvasive and noncontact biological information sensor. We believe that in the future, this method can be applied in clinical practice and that the use of a noninvasive, noncontact biological information sensor will help nurses determine a patient’s respiratory status.
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