Abstract
Heart rate (HR) and respiratory rate (RR) are important parameters for patient assessment. However, current measurement techniques require attachment of sensors to the patient’s body, often leading to discomfort, stress and even pain. A new algorithm is presented for monitoring both HR and RR using thermal imaging. The cyclical ejection of blood flow from the heart to the head (through carotid arteries and thoracic aorta) leads to periodic movements of the head; these vertical movements are used to assess HR. Respiratory rate is estimated by using temperature fluctuations under the nose during the respiratory cycle. To test the viability and feasibility of this approach, a pilot study was conducted with 20 healthy subjects (aged 18–36 and 1 aged 50 years). The study consisted of two phases: phase A (frontal view acquisitions) and phase B (side view acquisitions). To validate the results, photoplethysmography and thoracic effort (piezoplethysmography) were simultaneously recorded. High agreement between infrared thermography and ground truth/gold standard was achieved. For HR, the root-mean-square errors (RMSE) for phases A and B were 3.53 ± 1.53 and 3.43 ± 1.61 beats per minute, respectively. For RR, the RMSE between thermal imaging and piezoplethysmography stayed around 0.71 ± 0.30 breaths per minute (phase A). This study demonstrates that infrared thermography may be a promising, clinically relevant alternative for the assessment of HR and RR.
Highlights
Heart rate (HR) and respiratory rate (RR) are important vital signs used to assess the patient’s state; normal values for these two parameters vary according to age
The algorithm used to estimate HR is based on the cyclical ejection of blood from the heart to the head, which leads to periodic movements of the head
An approach has been presented for unobtrusive monitoring of two vital parameters, HR and RR, using Infrared thermography (IRT)
Summary
Heart rate (HR) and respiratory rate (RR) are important vital signs used to assess the patient’s state; normal values for these two parameters vary according to age. Sensors 2018, 18, 1541 chest-abdomen movement with respiratory belt transducers [2,3]; (2) measurement of electrical impedance of the thorax; or (3) computing the direct influence of breathing on ECG morphology (ECG-derived respiratory signal) or photoplethysmography (PPG) morphology [2]. These monitoring techniques are reliable and not costly, they require attachment of adhesive sensors on the patient, often leading to discomfort, stress, and even pain or soreness [4]. There are more precise (albeit more invasive techniques) to measure RR, such as capnography (assessment of partial pressure of carbon dioxide in exhaled air) and spirometry (assessment of variation in air flow) [2]
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