Cardiac Function

Cardiac  function  refers  to  the  contraction  of cardiac  muscle,  which  works  as  a  pump  to  send blood  throughout  the  circulatory  system  to  provide  adequate  blood  flow  to  organs  and  tissues. The heart achieves this by contracting its muscular through the aortic valve, into the aorta, and throughout the body. To accomplish this, the heart must  maintain  systolic  and  diastolic  blood  pressure and cardiac output (amount of blood ejected from the heart in one minute). Each time the heart beats,  a  volume  of  blood  is  ejected.  This  stroke volume (SV), times the number of beats per minute  (heart  rate  [HR]),  equals  the  cardiac  output (CO). Normal, resting CO differs among individuals  of  different  size.  The  resting  CO  of  someone who weighs 240 pounds is greater than the cardiac output found in a person who weighs 120 pounds. Thus, measured values for CO are expressed as a flow  (liters  per  minute  [L/min])  per  body  surface area (m2). When cardiac output is expressed in this way, it is termed cardiac index and has the units of L/min/m2. The surface area is estimated from calculations based on body weight and height (body surface area = 0.007184 x W0.425x H0.725). Cardiac index normally ranges from 2.6 to 4.2 L/min/m2.

There  are  numerous  measures  that  can  assess cardiac function. More extensive analyses include simple  and  noninvasive  to  more  complicated  and invasive  tests  of  cardiac  function.  Noninvasive tests  include  chest  x-ray  analysis,  electrocardiography  (ECG),  and  echocardiography.  Invasive tests  include  cardiac  catheterization,  Thallium scanning,  and  for  patients  with  coronary  artery disease,  pharmacologic  or  exercise  stress  ECG, pharmacologic  or  exercise  stress  myocardial  perfusion  imaging  (MPI),  electron  beam  computed tomography   (EBCT),   and   positron   emission tomography (PET). These techniques allow for the determination  of  global  cardiac  muscle  function analyses,  volumetric  analyses  (calculation  of  left ventricular functional parameters like end-diastole volumes  and  ejection  fraction),  and  regional  wall motion  abnormalities.  In  addition,  the  function of the heart as a pump can be determined by the force  of  ventricular  muscles  during  systole  and  is directly affected by the preload and contractility of the heart. Preload is the load on the cardiac muscle during  diastole  (relaxation).  This  preload  (enddiastolic  volume)  alters  the  ability  of  the  heart to  change  its  force  of  contraction  and  therefore increases stroke volume. This response to changes in venous return is called the Frank-Starling mechanism. Contractility can also be increased with an increase  in  calcium  release  into  the  cell.  This  can occur  in  response  to  catecholamines  (epinephrine and  norepinephrine),  which  are  released  by  the sympathetic nervous system. Cardiac activation is often  a  result  of  sympathetic  activation  from  the central nervous system.

Blood pressure indirectly provides a measure of cardiac  function.  As  blood  is  pumped  out  of  the left  ventricle  into  the  arteries,  pressure  is  generated. The mean arterial pressure (MAP; the average  pressure  within  an  artery  over  a  complete cycle  of  one  heartbeat)  is  determined  by  the  CO, systemic  vascular  resistance  (SVR),  and  central venous pressure (CVP): MAP = (CO × SVR) + CVP. At normal resting heart rates, MAP can be approximated by the following equation: MAP = DBP +1/3(SBP-DBP). MAP can indicate a level of cardiac function at rest.

In  sport  and  exercise  psychology,  measures of  cardiac  function  provide  specific  information regarding  the  effects  of  stress,  both  physical  and psychological,  on  cardiac  function.  Elevations  in cardiac  function  in  physically  healthy  individuals indicate  sympathetic  nervous  system  activation. This can occur in response to perceived threat in a competitive challenge or in response to meeting the physical demands of movement. In addition, measures of cardiac function are often used to identify the physiological demand or intensity of an activity. This can be done to ensure that the activity is appropriate  and  safe  and  to  examine  changes  in cardiac function following physical training, treatment, or an intervention.

References:

  1. Berntson, G. G., Quigley, K. S., & Lozano, D. (2007).Cardiovascular psychophysiology. In J. T. Cacioppo, L. G.Tassinary, & G. G. Berntson (Eds.), Handbook of psychophysiology (3rd ed., pp. 60–92). New York: Cambridge University Press.
  2. Boutcher, S. H., & Hamer, M. (2006). Psychobiological reactivity, physical activity, and cardiovascular health. In E. O. Acevedo & P. Ekkekakis (Eds.), Psychobiology of physical activity (pp. 161–176). Champaign, IL: Human Kinetics.
  3. Klabunde, R. E. (2012). Cardiovascular physiology concepts (2nd ed., pp. 60–99). Baltimore, MD: Lippincott, Williams & Wilkins.

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