Thursday, September 23, 2010

6.24 Control Your Blood Pressure & Heart Rate

Physician's Notebooks 6  - - See Homepage

24. Cardiovascular–Respiratory Control Techniques Update 19 December  2018
The following descending list of headings in order as they appear will help locate the reading by search & find or scrolling down.

 Stroke Volume (SV). The Cardiac Output 
Heart failure (HF)
Heart Rate and Major Pulses
Technique of feeling heartbeat and pulses
coarctation (bottleneck constriction) of aorta
Affect of Body Position
Respiratory Motions
Valsalva Maneuver (VM)
The use of Medication to Affect Hypertension & Tachycardia
Being In Touch with Your Cardiovascular-Respiratory System
Start of a heart arrhythmia
Extra Heartbeats or Palpitations
24-hr Holter monitor test
Focus on your heart’s power to contract and to push blood from left ventricle as a bulge pulse-wave that distends your aorta and moves forward into the arteries that branch from it. The strength of the heartbeat is how much it puts into the pulse of blood it ejects into the aorta, its Stroke Volume (SV). The Cardiac Output is the volume of blood in 1 minute of pulses, the Stroke Volume multiplied by Heart Rate (SV X HR). 
   If a normal Cardiac Output is not maintained, the brain suffers, you pass out, and if it continues for more than 5 minutes you die. At lesser levels of heartbeat weakness, vital organs like brain, kidneys and liver suffer most.
   Heart failure (HF) is the drop of Cardiac Output below the normal needed to maintain all organ systems.
   Every time you exercise, you must increase Cardiac Output because your muscles need the extra blood to get more oxygen and nutrients. But the increase of Cardiac Output may be at the cost of the oxygen needs of your heart muscle and brain, and it may put you at risk for deadly heart attack (myocardial infarction) or brain stroke (cerebral infarction).
   The heart’s response to a “request” for increasing Cardiac Output (eg, starting to jog) is to up its Stroke Volume and heartbeat rate. Part of increasing the SV is to take deep breaths, which draw in more blood, more quickly to fill the heart more. Within limits, the more the ventricles of heart fill before they contract, the greater the SV because of the tendency of heart muscle to contract more forcefully when passively stretched. But, as more and more blood fills the pre-contraction heart's left ventricle, it becomes less and less efficient to eject the blood into the aorta. This efficiency of ejection is called the Ejection Fraction (EF), which is the fraction of the pre-ejection volume of blood in the left ventricle that is ejected into the aorta. It is measured most easily by Echocardiogram. An EF of less than 50% (0.5) is Heart Failure. Most normal young, healthy hearts can achieve EF to 0.75.

Heart Rate and Major Pulses: Let us follow a single heartbeat pulse into the arteries. It originates in a heartbeat in left chest. The heartbeat starts in the squeeze of the left ventricle after it has filled up following the heartbeat. Then it ejects a pulse of blood into the ascending aorta that causes a pulse-bulge to travel up the aorta into and around its arch. At the arch its first branch distended by the pulse-bulge is the brachio-cephalic artery.   Just before the reaching right shoulder, the brachiocephalic artery artery divides into the right subclavian artery which passes to the right arm and becomes the right radial artery, and into the right carotid artery. The pulse of blood we are tracking in the arch of the aorta then moves forward and sends a bulge up the left carotid artery, whose pulse we feel in left side of neck, and immediately it sends a pulse down the left subclavian artery that makes the left radial pulse in left wrist. Then the remaining aortic pulse goes down the descending aorta and divides to go to the left and right femoral arteries you feel as pulses in both thighs. If you could actually measure in milliseconds the pulse originating from the single heartbeat, it would be detected, in order, in right neck carotid, left neck carotid, right wrist radial, left wrist radial and over left and right femoral arteries. In practice by feeling the pulses the time differences are undetectable.
   The power of a single pulse is measured as blood pressure and it roughly transmits to a feeling of strength of a palpated pulse. It is not accurate to estimate BP from the feeling of a pulse but very low BP in a person about to faint will give a weak pulse to the palpating finger while very high BP will give a too strong pulse. Strength of pulse feeling depends much on the difference between systolic and diastolic BP called the pulse pressure. The wider that difference, the sharper and stronger and more discrete will be the pulse. In the extreme, as with a hole or opening in an aortic valve or a major hole between the aorta and a major vein or pulmonary artery, the high pulse pressure gives a pulse called pistol shot.
   The power of a single pulse diminishes as the pulse moves forward. Thus if size and location of arteries are same, as in wrist pulses, the right pulse should be slightly stronger than the left because it is closer to the power source. It may be noted in your right arm BP being a few millimeters Hg (mercury column in BP machine) higher than your left arm BP.

Technique of feeling heartbeat and pulses: On wrist, use tips of 2nd and 3rd fingers of opposite hand rolled back and forth on inner side distal-end of radius bone where hand meets forearm at wrist and you should feel the radial pulse. In neck, the carotid pulses are easily felt by placing thumb and forefinger of either hand under angles of jaw and gently pressing in with tip of finger. The femoral pulse is felt by pressing 2nd and 3rd fingers just below inguinal ligament at midpoint in front thigh. 
   The femoral pulse, because large size artery and superficial location with firm muscle and bone behind, may give stronger pulse than wrist pulses. If wrist pulse is stronger feeling than femoral pulse, it is abnormal and may mean coarctation (bottleneck constriction) of aorta and should be brought to a doctor’s attention.
   The heartbeat rate is most accurately got by counting the heartbeat or pulse for 60 seconds. You may also count for 5 seconds and multiply by 12 or for 10 sec. x 6 or 15 sec. x 4. Sometimes you need the shortest count for near simultaneous comparison of heartbeat rate and pulse rate from wrist. Normally the heartbeat rate and the pulse rate should be the same but sometimes you may notice that the pulse rate is less than the heartbeat rate and it either means a cardiac arrhythmia, usually atrial fibrillation, or a seriously failing heart that beats on again off again too weakly to always transmit to wrist pulse.

Affect of Body Position: Assuming quiet, resting condition with same breathing; if you lie down flat compared to sitting or standing, you will increase return of blood to heart from lower part of body while only slightly changing return from upper part. Heart will then fill up with more blood just before squeezing and Stroke Volume (SV) will increase. This may be good if you need to increase cardiac output (i.e., in near faint condition) but it also gives the heart more work to do, and that could be not so good if you are just having heart attack myocardial infarction. Best position for conserving the heart’s work, while maintaining adequate cardiac output (as in Myocardial Infarction or heart failure) is lying down with feet below the knees so as to moderately reduce return of blood in the supine state from the lower body to heart.

What about standing up? By assuming erect position, you suddenly slow the return of lower body venous blood to Heart which should drop cardiac output. It often does and explains why a person may feel faint after standing up. But most persons do not faint because the initial drop of BP in aorta is sensed and the neurotransmitter, hormone norepinephrine is quickly released by sympathetic nerve endings and epinephrine released by adrenal gland and it speeds heart, constricts arteries and veins, and reverses the dropping BP and cardiac output so that after standing up the BP rises slightly in normal state.
   Squatting has been noted to be a natural reaction of children to heart failure. It makes Heart more efficient by markedly increasing the resistance to arterial blood flow at knees and thus decreasing the working volume for the heart and circulation. The increased arterial resistance in the aorta plays back on the left ventricle, causing it fill more and to contract more efficiently and also the cardiac output is more efficient to provide oxygen and nutrients to vital organs especially brain and heart because it is working with a smaller effective arterial blood space, involving mostly middle of body and upper extremities and head. So do not forget about squatting when you feel faint or have shortness of breath from heart failure and no place to lie down. (Like in crowded train or bus)
   One way of preventing fainting caused by standing up is to rapidly contract and relax calf muscles, which will produce muscle pump action on veins of legs and speed return of blood to heart. Also lower head and raise arms.

Respiratory Motions: In the chest are the lungs, heart and great vessels that include the big thin-wall vena cava and azygos veins. These big veins carry body venous blood into right side of heart. These are air-tightly encased in a chest cavity that can be contracted and expanded like a bellows. 
   As long as there is no obstruction to passage of air from mouth and nostrils in and out of inner lung, much of the positive and negative chest cavity pressure of breathing motions is transmitted to expand and collapse the lungs. But even then, some negative pressure acts on the thin-walled big veins and sucks blood faster into the right side of heart during an inhalation (breathing-in). This extra filling of the right heart ventricle causes it to beat more powerfully to expel more blood into the pulmonary arteries going to lungs. But the deep inspiration also stretches out the thin wall pulmonary blood vessels causing the extra blood to pool in the lungs so actually the overall effect of a deep inhalation is to only slightly increase stroke volume (SV) of left ventricle. But breathing-in speeds the heart rate so the overall cardiac output from heart to aorta is upped in a deep inspiration. Oppositely, the exhalation (breathing-out) motions cause pressure on venous return to heart and on the pulmonary blood vessels and slow the heart by reflex effect and reduce the cardiac output.
   Now, this breathing effect will be markedly enhanced if you block off your airway, which everybody does when they strain on toilet or cough or sneeze. Actually there is a maneuver – the Valsalva Maneuver (VM), where you make an exhaling effort but prevent the exhalation of air from lungs by closing off your airway and it is part of straining on toilet. The effect of Valsalva is complex and also involves hormone reflex but overall in the 30 seconds after you do a Valsalva, you will drop the BP. Doing a Valsalva at same time as a doctor or nurse starts taking your BP and timing it to extend to just as the BP is being recorded on the machine may briefly drop the BP reading as much as 20 systolic. (Before trying this, check the timing by doing the maneuver and taking the BP on your digital BP machine).

More about Valsalva Maneuver and the Effect of Cough and Sneeze: Every day we all do the VM many times sitting on toilet, straining at BM, coughing, sneezing, straining to lift. But we rarely think what it is causing in chest and brain and heart. Some of us are young and healthy so we tolerate sudden short rises or drops of arterial blood pressure and slowing or speeding of heart rate and shocks of re-echoing pulse waves of blood that go back along the vena cavae and the jugular veins with each Valsalva. But an unlucky older person with weak blood vessel in brain may burst it from one strong Valsalva and get brain hemorrhage stroke or, with a narrowed coronary artery in heart, may stagnate the flow through it and clog it causing a myocardial infarction heart attack or a narrowed cerebral artery to clog and cause thrombotic brain stroke. It is cause of collapse in bathroom. How to prevent? First keep aware of it and you can markedly cut frequency and strength of a Valsalva. Instead of straining at stool strongly, do it mildly if at all; and if no success stop straining and use your finger into anus-rectum to get out the stool. In urination, especially old men with prostate blockage, don't strain; just give it time or, if you see you’re filling with pee, press fist deep into low abdomen. And as you feel you need to cough or sneeze, you should open mouth and sit down in order to dissipate the positive pressure wave from the Valsalva caused by coughing or sneezing.
The use of Medication to Affect Hypertension &Tachycardia I have been taking Bisoprolol, a beta blocker, 5 mg daily for years.  I do not really have hypertension but my resting heart rate tends to be high because I am a bit of a hyper personality. So I decided to take the beta blocker to give a more healthy slower resting heart rate.  Also the beta blocker, weakens the heart muscle; not enough to cause heart failure in a normal heart but enough to drop the blood pressure from higher to lower healthy levels. Recently I used up my Bisoprolol supply before I could get a new Rx and after being off the pills for a week I checked my blood pressure and heart rate and - Lo! - I got 175/115 and 91 bpm! Those are not levels that give healthy longevity. I immediately got a new supply and within hours of taking my usual 5 mg dose the BP was back to 120/70 and HR 67 bpm, around the usual on the medication. This shows an effect of supersensitivity.  The beta receptors on the natural heart pacemaker cells, after years of being blocked by the medication, have increased in numbers hugely so that if one suddenly stops the medication, one gets a hypersensitivity to all the stimuli that cause an excessively rapid heart rate. Also the beta receptors on the heart muscle cells increase markedly and on stopping the pill, the blood pressure shoots up because of increased heart power. In addition to proving the usefulness of beta blocker medication for achieving a low normal heart rate and low normal blood pressure, the sudden stopping of a usual dose beta blocker (5 mg a day Bisoprolol et al) after a week or two of use can cause a state of hypertension and tachycardia that could get one refused from military service.  
Being In Touch with Your Cardiovascular-Respiratory System (CV-RS): First, just be aware of feelings of pulsation around head or in chest. They come briefly due to temporary rises in arterial BP. A good example you can test is from coffee on empty stomach in quiet condition. Try it tomorrow morning and you should note within a minute a pulsation around head. Such pulsations ought always to be brief and regular; they are coming from the heartbeat. If irregular, so is the heartbeat. A type of secondary curable high blood pressure (tumor of adrenal gland) comes on as attacks of sudden high BP; an alerted person will hear it in head. 
Also be aware of sinus arrhythmia - the speeding of your pulse during a breathe in and its slowing as you breathe out. Young persons sometimes note this in a marked way and, if they are not aware it is a normal response of the heart to breathing, they get very neurotic over it. 
  Start of a heart arrhythmia ought to be detected by alert person (You, after reading this!) feeling the start of an irregularity in chest. A non alert person goes for days with dangerous arrhythmia and ends with stroke. 
  Extra Heartbeats or Palpitations: Even with simple single palpitation of Heart, it is useful to be alert to the feeling. The single jump or bump is actually not the extra heartbeat, it is the more powerful normal rhythm heartbeat that follows after the abnormally timed extra-beat – powerful because the ineffective extra heartbeat delays the next normal beat and allows Heart to fill up more than usual before its next squeeze and thus increases power of that squeeze. Being aware of this is reassuring but when it happens several or more a day, a 24-hr Holter monitor test should be done because extra beats of certain type predict sudden death syndrome or atrial fibrillation.
   Now you know how to feel pulses, you may check each morning and night in bed or whenever you get a sense of your heart beating abnormally. Using a digital BP machine, you should relate the BP number you measure on the machine and the feel of the pulses under your finger. Then experiment around with Valsalva and timings and positions as I have suggested. In that way you can come to control your blood pressure and also to estimate it from feeling your pulses. (But once you have succeeded in these experiments, stop the frequent checking BP and pulse because you do not want it to become a neurotic habit and a cause for paranoia about your heart) 
  End of Chapter. To read next now, click 6.25 High Altitude, Underwater, High Temp Affect ...


handspring said...

Thanks, nice explanation. I like what you're doing.

handspring said...

I must read some more.