PHYSIOLOGICAL EFFECTS OF VALSALVA AND IPPV

DR. H. P. S. N. ALWIS

Consultant anaesthetist

B. H. Negombo

Valsalva Maneuver

• 1707- Italian anatomist Valsalva discribed this maneuver.

• The subject closes the mouth and nose, expires forcibly and thereby increases the pressure inside the pharynx and the lung passages.

• Today this is used to asses the autonomic responsiveness to circulatory changes.

• Increased intrathoracic pressure red. VR red.C.O. red. BP

Procedure

• The subject expires against a 40 mm Hg resistance for 15 sec.

• Sudden inc. ITP. / intra abd. Pressure /CSF pressure

• The peripheral venous valves shutthe blood accumulate in peri. Veins aortic flow drops to about 50% of control.

Four Phases 0f Valsalva

1. Inc. ITP transmitted to aorta and arterial tree Inc. arterial pressure reflex red. in HR

2. Red. VR red. Mean arterial pressure reflex inc. in HR peri. Vasoconstriction3. Immediately after release sudden red.ITP red.BP

inc. HR4. Rapid surge of VR marked inc.BP marked red. HR (diagram)Similar response in lifting, pushing, coughing etc.

Four Phases of Valsalva

Abnormal Valsalva Responses

• 1. Increased intrathoracic blood volume – “square wave” response eg. CCF

• 2. Patients with stiff lungs – absent response

• 3. Autonomic insufficiency – blocked Valsalva– eg. Primary idiopathic hypotension

• 4. Primary hyperaldosteronism – blocked Valsalva (diagram)

Abnormal Valsalva Responses

Abnormal Valsalva Responses

IPPV

• 1543-Vesalius –animal research• 18th century - human research• 1952 - >200 cases of poliomyalitis

treated with IPPV • Tremendous use in anaesthetic practice

and management of critically ill• But ass. with disturbances in normal

physiological mechanisms

IPPV ctd.

• Normal breathing – negative pressure in the intrapleural space during insp.

• IPPV – positive pressure in the upper airways pushes gas in.

• This positive intrathoracic pressure is responsible for most of the physiological disturbances.

Systems Affected

• 1. Res.system 2 . CVS

• 3. Renal 4. Brain 5. GIT

6. Endocrine

7. Metabolic

Res. System

• 1. Red. FRC • 2. Altered distribution of vent.• 3. Inc. shunt effect• 4. Inc. dead space• 5 Barotrauma• 6. Redistribution of extravascular lung

water• .

FRC• FRC – vol.of gas in the lungs at the end of normal exp.

• FRC is reduced by about 17% in the adult with anaes. and muscle relaxation • The most likely reason is cephalad displacement of the

diaphragm and alteration of thoracic geometry• .• Red. FRC encroachment of closing capacity areas of

atelectasis inc. shunt [ diagram]

• Abd. Distension and prone position – marked red. FRC

Artificial Ventilation of the Lungs

Distribution of Vent.

• In the normal person compliance is greatest in the most dependent parts of the lungs due to the variation in the resting volume of different lung units.[diagram]

• In the supine patient expansion of most dependent part of the lung is opposed by the pressure of the abd. contents.

• But in spon.breathing pt.inc. contractility of those parts of the diaphragm compressed by the abd. Contents counteracts this.

• During IPPV this does not happen. Therefore insp. gases preferentially distributed to uppermost lung units.

• Prone position –dorsal part, lat. Position -uppermost

Disribution of Vent. ctd.

• Time constant • TC = resistance x compliance units

with short TC fill and empty rapidly. (fast alveoli) units with long TC fill and empty slowly. (slow alveoli)

• Variation in insp. and exp. time can affect distribution of ventilation. Eg. Short insp time favours fast alveoli. Long insp. time favors slow alveoli. Short exp. time in slow alveoli incomplete emptying barotrauma. This is important in diseased lungs.

Increased Shunt Effect

• Red. FRC red. dependent lung vent. inc. vent. In the nondependent lung

• .

• But perfusion is reduced in the nondependent lung and further red. In perfusion due to red. CO with IPPV.

• This leads to inc. V/Q mismatch.

Increased Dead Space

• The regional perfusion of the lung is gravity dependent.

• In the apical region alv.p > pul. Art.p.>pul.ven.p low perfusion in the apices

• IPPV overdistension of apical alveoli inc. VD/VT ratio.

Barotrauma

• Large TV and excessive inflation pressures increases the risk of barotrauma.

• Peak airway pressure > 30 cm H2O pul.interstitial emphysema.

• Peak awp. > 60 cm pneumothorax• More common in -

- nonuniform lung diseases - - obs. airways disease - broncho pul. dysplasia -hypovolaemia

Other effects - Absent cough - Absent sigh effect - Impaired clearence of secretions

Redistribution of lung water IPPV inc. pul. Cap. P inc. p. gradient inc. fluid This is not clinically significant.

In pul. oedema IPPV redistribution of lung water, recruitment of alveoli and reopening of airways improved gas exchange

Cardiovascular System

• The main effect is red. CO (10 – 20%)

• This is due to 1. red. VR 2. inc. pul. Vas. resistance 3. red. LV compliance 4. cardiac tamponade effect 5. Release of a negative inotropic factor

Venous Return

• Spon. Insp. red. ITP inc. VR - keeps the atria open

• IPPV inc. ITP during insp. red. VR• In a poorly compliant lung inc. airway p.is

not transmitted to intrapleural space and red. CO is less.

• The effect of anaes. and sedative drugs further compromise the BP.

Pulmonary Vascular Resistance

• IPPV expansion of alveoli constriction of small bid. Vessels inc. resistance.

• Larger vessels are tethered to the co. tissue inc. calibre.

• Net effect is inc. pul. Vas. resistance.• In the presence of lung path.

IPPV inc. FRC red. hypoxic pul. vasoconstriction

LV Compliance

• Inc. pul. vas. resistance inc. RV afterload red. RV output dilatation of RV deviation of interventricular septum to the left red. LV size red. CO

• Inc. RV afterload red. LA filling red. LV output

• Elderly and hypovolaemic patients have a higher risk. cardiac tamponade effect and negative inotropic effect – demonstrated in animals.

Renal System

• IPPV red. UOP - Na retention

• This may be due to 1. red. CO

2. hormonal changes• Red. CO red. Renal perfusion p.

Red. VR inc. renal venous p. Red. A-V p.gradient red. perfusion.

• Hormonal changes 1. red. Anti Natriuretic Factor 2. inc. renin activity 3. inc. ADH

Brain Red. VR inc. ICP Hypervent. red. Paco2 constriction of cerebral bld. vessels

red. ICP. GIT Paralytic ileus lasting for about 48 hrs. May be due to red. gut perfusion or altered autonomic activity.

Metabolic functions IPPV might have an effect on the hormone synthesis and met. which

take place in the lungs.

PEEP and CPAP exaggerates all above physiological effects.