Validity and Reliability of a Clinical Method for Assessment of Cardiorespiratory Fitness Using Seismocardiography
Condition: Cardiorespiratory Fitness Test
Study type: Observational

Summary: 
      Measurement of cardiorespiratory fitness (here VO2max) is considered a valuable tool for
      improving the risk prediction of cardiovascular disease and overall patient management.
      However, the gold standard method for determining VO2max requires both maximal exercise until
      exhaustion and expensive equipment, why it is not always feasible. A new method for
      estimating VO2max using a non-exercise prediction model with seismocardiography (SCG)
      information has been proposed. SCG is recording and interpretations of vibrations originating
      from the beating heart measured on the chest wall with an accelerometer. SCG has previously
      been shown to correlate to physiologic events in the cardiac cycle and thus a measure of
      cardiac performance. VO2max is generally believed to be limited by the rate of oxygen
      delivery to the muscles, where maximal cardiac output and oxygen carrying capacity of the
      blood are considered the main limiting factors. The theoretical basis for incorporating SCG
      to a VO2max prediction model is therefore evident. The previous studies assessed the
      prediction model in a cross-sectional study design to compare validity of the method. A
      requirement of further validation of the prediction model with reliability assessment is
      therefore needed.

      Biological age is a concept trying to relate the age to the health status rather than the
      date of birth. Biological age assesses the heterogeneity in functional metabolic status and
      vulnerability to disease. A Biological age model has previously been designed for health
      promotion interventions. However, reliability assessment of the model is needed.

      The purpose of the current study was therefore to:

        1. investigate the validity and reliability of a new clinical method for estimation of
           maximal oxygen consumption (VO2max) using seismocardiography.

        2. investigate the reliability of the biological age model.
    

Detailed description: 
      20 healthy participants were recruited for the study. The study included three identical
      visit to the laboratory within 14 days.

      The participants received both written and oral information about the study and the possible
      risks associated hereof, before volunteering and signing a written informed consent form.

      The participants arrived at the laboratory after an overnight fast from latest 10pm the day
      before (water excepted). Furthermore, the participants were asked to avoid strenuous exercise
      48 hours prior to the test day and eat a habitual diet, which had to be replicated before the
      second and third visit.

      Testing at each visit to the laboratory included:

      Completion of a short version of the International Physical Activity Questionaire, about
      leisure time physical activities.

      Measurements of height, weight and waist and hip circumference.

      Measurement of body composition using a Dual-energy X-ray absorptiometry (DXA) scan on day 1.

      Measurement of body composition using a bioelectrical impedance analysis scale on day 1, 2
      and 3.

      Measurement of blood pressure in the supine position. 3 measures with 2 minute resting in
      between.

      Measurement of VO2max using a non-exercise testing method based on seismocardiography.

      Collection of a 15 ml resting venous blood sample for measurements of resting levels of
      hormones, metabolites and lipids in the blood plasma.

      Measurement of lung function in terms of FEV1 and FVC (Vyntus SPIRO spirometer, Vyaire
      Medical).

      Determination of VO2max applying a graded exercise test on a bicycle ergometry until
      voluntary exhaustion with continuous pulmonary gas exchange measurements.

      Procedure and analysis:

      Bioelectrical impedance analysis scale (Tanita MC-780MA, Tanita Corporation of America Inc):
      The participants was analysed on the scale after voiding and wearing minimal clothing.

      DXA scanning (Lunar iDXA, GE Healthcare): The participants was placed in the supine position
      in the DXA scanner after voiding and while wearing minimal clothing.

      Blood samples: The blood samples was collected from the vein cubiti medialis in the forearm.
      The blood was sampled in iced BD vacutainers (5 mL Aprotinin, 4 mL EDTA and 2 mL Lithium
      Heparin) and immediately centrifuged at 4000 g for 10 minutes at 4⁰C (Rotina 380R, Hettich).
      The plasma was collected and stored at -80⁰C for later analyzes of resting levels of
      metabolites, lipids and hormones.

      The concentrations of hemoglobin, hematocrit, glucose and lactate was immediately analyzed
      though sampling of 2 mL blood in a specialized syringe (safePICO Aspirator, Radiometer) and
      using an automatic analyzer (ABL800 Flex, Radiometer).

      SCG VO2max prediction:

      The SCG VO2max prediction was performed as previously described with the same type of
      equipment. Brief, the SCG recording was performed using an iWorx IX-228/s (IWORX, Dover, New
      Hampshire) connected to a PC. LabScribe was used as recording software (version 3. Dover, New
      Hampshire). The accelerometer (Silicon Design 1521-002) had a resolution of ± 2 g, a low
      noise at 7 μg / √ Hz and a frequency 70 response of 0-300 Hz and was placed on sternum 2 cm
      proximal of processus xiphoideus. The recording lasted 5 minutes and was performed in the
      supine position. VentriJect Aps later performed the signal processing and VO2max estimation.
      VentriJect Aps was informed of the age, height and weight of the participants for inclusion
      in the prediction model, but was blinded of the measured VO2max.

      Hereafter a new devolved wireless device (Seismofit, VentriJect Aps) was used to determine
      SCG VO2max. The Seismofit contains a 3v battery and a three-axis digital output accelerometer
      (LIS3DHH, ST Microelectronics). The Seismofit device is connected to a phone application
      where the participants demographic data (age, height and weight) was entered before
      performing the recording. For the recording, the participants was lying in the supine
      position and the Seismofit device was placed on sternum 2 cm proximal of processus Xiphoideus
      with double adhesive tape. The predicted SCG VO2max value appeared on the phone screen within
      5 minutes.

      The Seismofit VO2max prediction was performed twice with 5 minutes rest in between. This was
      done to assess the test-retest reliability of the device.

      The iWorx VO2max was done to compare the previous equipment with the new wireless equipment
      with automatic signal processing.

      The gold standard VO2max determination:

      A graded exercise test (GET) until voluntary exhaustion on a bicycle ergometer was performed.
      The protocol consisted of a five-minute warm-up at 80 W for women and 100 W for men and
      increased hereafter with 20 W for women and 25 W for men every minute until exhaustion.

      Participants was wearing a chest strapped heart rate monitor (Polar Vantage XL, Polar) with
      continuous heart rate measures during the test. Furthermore the participants, was asked about
      perceived exhaustion on the 6-20 Borg scale directly following exhaustion.

      Statistical analysis:

      All data was checked for normal distribution (Shapiro-Wilk test) and equal variance (Brown-
      Forsythe test). The significant level is p<0.05.

      A Mixed-effect model, Bland-Altman analysis with 95% limits of agreement, Pearson
      correlations and Mean Absolute Percentage Error was used for assessment of validity between
      the Seismofit VO2max and GET VO2max, Seismofit VO2max measure 1 and 2 and between Seismofit
      VO2max and iWorx VO2max.

      Coefficient of Variation (CV), Standard Error of Estimate (SEE) and Intraclass Correlation
      Coefficient (ICC) was used to assess reliability of VO2max measurements.

      The project was approved by the Science Ethical commitee of the greater region of Copenhagen
      (H-19081375) the 3rd of February 2020. The protocol of the study adhered to the principles of
      the Helsinki declaration.
    

Intervention name(s): VO2max validity and reliability assesment
Intervention type(s): Other
Intervention description(s): Reliability assessment of VO2max determination with three repeated measures for two methods.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        A representative selection of the healthy adult population
      
Biospecimen description: 
      Blood samples
    
Keywords: Validity; Reliability; VO2max testing; Biological age